diff --git a/src/FactorGraphs/DefaultVariable.php b/src/FactorGraphs/DefaultVariable.php
index 8544d7a..96cc5f0 100644
--- a/src/FactorGraphs/DefaultVariable.php
+++ b/src/FactorGraphs/DefaultVariable.php
@@ -17,7 +17,7 @@ class DefaultVariable extends Variable
         return null;
     }
 
-    public function setValue($value)
+    public function setValue($value): never
     {
         throw new Exception();
     }
diff --git a/src/FactorGraphs/Factor.php b/src/FactorGraphs/Factor.php
index d915769..c64bbe3 100644
--- a/src/FactorGraphs/Factor.php
+++ b/src/FactorGraphs/Factor.php
@@ -6,15 +6,15 @@ use DNW\Skills\Guard;
 use DNW\Skills\HashMap;
 use Exception;
 
-abstract class Factor
+abstract class Factor implements \Stringable
 {
-    private $_messages = [];
+    private array $_messages = [];
 
     private $_messageToVariableBinding;
 
     private $_name;
 
-    private $_variables = [];
+    private array $_variables = [];
 
     protected function __construct($name)
     {
@@ -111,7 +111,7 @@ abstract class Factor
         return $message;
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return $this->_name;
     }
diff --git a/src/FactorGraphs/FactorGraphLayer.php b/src/FactorGraphs/FactorGraphLayer.php
index 43673fb..2aa8c62 100644
--- a/src/FactorGraphs/FactorGraphLayer.php
+++ b/src/FactorGraphs/FactorGraphLayer.php
@@ -5,17 +5,14 @@ namespace DNW\Skills\FactorGraphs;
 // edit this
 abstract class FactorGraphLayer
 {
-    private $_localFactors = [];
+    private array $_localFactors = [];
 
-    private $_outputVariablesGroups = [];
+    private array $_outputVariablesGroups = [];
 
     private $_inputVariablesGroups = [];
 
-    private $_parentFactorGraph;
-
-    protected function __construct(FactorGraph $parentGraph)
+    protected function __construct(private readonly FactorGraph $_parentFactorGraph)
     {
-        $this->_parentFactorGraph = $parentGraph;
     }
 
     protected function getInputVariablesGroups()
diff --git a/src/FactorGraphs/FactorList.php b/src/FactorGraphs/FactorList.php
index 6d3bcd7..e25138c 100644
--- a/src/FactorGraphs/FactorList.php
+++ b/src/FactorGraphs/FactorList.php
@@ -7,7 +7,7 @@ namespace DNW\Skills\FactorGraphs;
  */
 class FactorList
 {
-    private $_list = [];
+    private array $_list = [];
 
     public function getLogNormalization()
     {
@@ -33,7 +33,7 @@ class FactorList
         $sumLogS = 0;
 
         foreach ($list as &$currentFactor) {
-            $sumLogS = $sumLogS + $currentFactor->getLogNormalization();
+            $sumLogS += $currentFactor->getLogNormalization();
         }
 
         return $sumLogZ + $sumLogS;
diff --git a/src/FactorGraphs/KeyedVariable.php b/src/FactorGraphs/KeyedVariable.php
index d48962e..465e10b 100644
--- a/src/FactorGraphs/KeyedVariable.php
+++ b/src/FactorGraphs/KeyedVariable.php
@@ -4,12 +4,9 @@ namespace DNW\Skills\FactorGraphs;
 
 class KeyedVariable extends Variable
 {
-    private $_key;
-
-    public function __construct($key, $name, $prior)
+    public function __construct(private $_key, $name, $prior)
     {
         parent::__construct($name, $prior);
-        $this->_key = $key;
     }
 
     public function getKey()
diff --git a/src/FactorGraphs/Message.php b/src/FactorGraphs/Message.php
index 9fbeadc..dfd1800 100644
--- a/src/FactorGraphs/Message.php
+++ b/src/FactorGraphs/Message.php
@@ -2,16 +2,10 @@
 
 namespace DNW\Skills\FactorGraphs;
 
-class Message
+class Message implements \Stringable
 {
-    private $_name;
-
-    private $_value;
-
-    public function __construct($value = null, $name = null)
+    public function __construct(private $_value = null, private $_name = null)
     {
-        $this->_name = $name;
-        $this->_value = $value;
     }
 
     public function getValue()
@@ -24,7 +18,7 @@ class Message
         $this->_value = $value;
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return (string) $this->_name;
     }
diff --git a/src/FactorGraphs/Schedule.php b/src/FactorGraphs/Schedule.php
index 64a5fbe..79ae6af 100644
--- a/src/FactorGraphs/Schedule.php
+++ b/src/FactorGraphs/Schedule.php
@@ -2,19 +2,16 @@
 
 namespace DNW\Skills\FactorGraphs;
 
-abstract class Schedule
+abstract class Schedule implements \Stringable
 {
-    private $_name;
-
-    protected function __construct($name)
+    protected function __construct(private $_name)
     {
-        $this->_name = $name;
     }
 
     abstract public function visit($depth = -1, $maxDepth = 0);
 
-    public function __toString()
+    public function __toString(): string
     {
-        return $this->_name;
+        return (string) $this->_name;
     }
 }
diff --git a/src/FactorGraphs/ScheduleLoop.php b/src/FactorGraphs/ScheduleLoop.php
index 4b875d6..7ae5475 100644
--- a/src/FactorGraphs/ScheduleLoop.php
+++ b/src/FactorGraphs/ScheduleLoop.php
@@ -4,15 +4,9 @@ namespace DNW\Skills\FactorGraphs;
 
 class ScheduleLoop extends Schedule
 {
-    private $_maxDelta;
-
-    private $_scheduleToLoop;
-
-    public function __construct($name, Schedule $scheduleToLoop, $maxDelta)
+    public function __construct($name, private readonly Schedule $_scheduleToLoop, private $_maxDelta)
     {
         parent::__construct($name);
-        $this->_scheduleToLoop = $scheduleToLoop;
-        $this->_maxDelta = $maxDelta;
     }
 
     public function visit($depth = -1, $maxDepth = 0)
diff --git a/src/FactorGraphs/ScheduleSequence.php b/src/FactorGraphs/ScheduleSequence.php
index 2c16e02..e16b5bc 100644
--- a/src/FactorGraphs/ScheduleSequence.php
+++ b/src/FactorGraphs/ScheduleSequence.php
@@ -4,12 +4,9 @@ namespace DNW\Skills\FactorGraphs;
 
 class ScheduleSequence extends Schedule
 {
-    private $_schedules;
-
-    public function __construct($name, array $schedules)
+    public function __construct($name, private readonly array $_schedules)
     {
         parent::__construct($name);
-        $this->_schedules = $schedules;
     }
 
     public function visit($depth = -1, $maxDepth = 0)
diff --git a/src/FactorGraphs/ScheduleStep.php b/src/FactorGraphs/ScheduleStep.php
index 0fc8fa2..98378d4 100644
--- a/src/FactorGraphs/ScheduleStep.php
+++ b/src/FactorGraphs/ScheduleStep.php
@@ -4,22 +4,15 @@ namespace DNW\Skills\FactorGraphs;
 
 class ScheduleStep extends Schedule
 {
-    private $_factor;
-
-    private $_index;
-
-    public function __construct($name, Factor $factor, $index)
+    public function __construct($name, private readonly Factor $_factor, private $_index)
     {
         parent::__construct($name);
-        $this->_factor = $factor;
-        $this->_index = $index;
     }
 
     public function visit($depth = -1, $maxDepth = 0)
     {
         $currentFactor = $this->_factor;
-        $delta = $currentFactor->updateMessageIndex($this->_index);
 
-        return $delta;
+        return $currentFactor->updateMessageIndex($this->_index);
     }
 }
diff --git a/src/FactorGraphs/Variable.php b/src/FactorGraphs/Variable.php
index cd89eab..5c6512d 100644
--- a/src/FactorGraphs/Variable.php
+++ b/src/FactorGraphs/Variable.php
@@ -2,18 +2,15 @@
 
 namespace DNW\Skills\FactorGraphs;
 
-class Variable
+class Variable implements \Stringable
 {
     private $_name;
 
-    private $_prior;
-
     private $_value;
 
-    public function __construct($name, $prior)
+    public function __construct($name, private $_prior)
     {
         $this->_name = 'Variable['.$name.']';
-        $this->_prior = $prior;
         $this->resetToPrior();
     }
 
@@ -32,7 +29,7 @@ class Variable
         $this->_value = $this->_prior;
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return $this->_name;
     }
diff --git a/src/FactorGraphs/VariableFactory.php b/src/FactorGraphs/VariableFactory.php
index af683a6..c20c73f 100644
--- a/src/FactorGraphs/VariableFactory.php
+++ b/src/FactorGraphs/VariableFactory.php
@@ -4,27 +4,21 @@ namespace DNW\Skills\FactorGraphs;
 
 class VariableFactory
 {
-    // using a Func<TValue> to encourage fresh copies in case it's overwritten
-    private $_variablePriorInitializer;
-
-    public function __construct($variablePriorInitializer)
+    public function __construct(private $_variablePriorInitializer)
     {
-        $this->_variablePriorInitializer = $variablePriorInitializer;
     }
 
     public function createBasicVariable($name)
     {
         $initializer = $this->_variablePriorInitializer;
-        $newVar = new Variable($name, $initializer());
 
-        return $newVar;
+        return new Variable($name, $initializer());
     }
 
     public function createKeyedVariable($key, $name)
     {
         $initializer = $this->_variablePriorInitializer;
-        $newVar = new KeyedVariable($key, $name, $initializer());
 
-        return $newVar;
+        return new KeyedVariable($key, $name, $initializer());
     }
 }
diff --git a/src/GameInfo.php b/src/GameInfo.php
index 3c77b84..1726895 100644
--- a/src/GameInfo.php
+++ b/src/GameInfo.php
@@ -7,37 +7,18 @@ namespace DNW\Skills;
  */
 class GameInfo
 {
-    const DEFAULT_BETA = 4.1666666666666666666666666666667; // Default initial mean / 6
+    final const DEFAULT_BETA = 4.1666666666666666666666666666667; // Default initial mean / 6
 
-    const DEFAULT_DRAW_PROBABILITY = 0.10;
+    final const DEFAULT_DRAW_PROBABILITY = 0.10;
 
-    const DEFAULT_DYNAMICS_FACTOR = 0.083333333333333333333333333333333; // Default initial mean / 300
+    final const DEFAULT_DYNAMICS_FACTOR = 0.083333333333333333333333333333333; // Default initial mean / 300
 
-    const DEFAULT_INITIAL_MEAN = 25.0;
+    final const DEFAULT_INITIAL_MEAN = 25.0;
 
-    const DEFAULT_INITIAL_STANDARD_DEVIATION = 8.3333333333333333333333333333333; // Default initial mean / 3
+    final const DEFAULT_INITIAL_STANDARD_DEVIATION = 8.3333333333333333333333333333333;
 
-    private $_initialMean;
-
-    private $_initialStandardDeviation;
-
-    private $_beta;
-
-    private $_dynamicsFactor;
-
-    private $_drawProbability;
-
-    public function __construct($initialMean = self::DEFAULT_INITIAL_MEAN,
-                                $initialStandardDeviation = self::DEFAULT_INITIAL_STANDARD_DEVIATION,
-                                $beta = self::DEFAULT_BETA,
-                                $dynamicsFactor = self::DEFAULT_DYNAMICS_FACTOR,
-                                $drawProbability = self::DEFAULT_DRAW_PROBABILITY)
+    public function __construct(private $_initialMean = self::DEFAULT_INITIAL_MEAN, private $_initialStandardDeviation = self::DEFAULT_INITIAL_STANDARD_DEVIATION, private $_beta = self::DEFAULT_BETA, private $_dynamicsFactor = self::DEFAULT_DYNAMICS_FACTOR, private $_drawProbability = self::DEFAULT_DRAW_PROBABILITY)
     {
-        $this->_initialMean = $initialMean;
-        $this->_initialStandardDeviation = $initialStandardDeviation;
-        $this->_beta = $beta;
-        $this->_dynamicsFactor = $dynamicsFactor;
-        $this->_drawProbability = $drawProbability;
     }
 
     public function getInitialMean()
diff --git a/src/HashMap.php b/src/HashMap.php
index aca2315..b45056c 100644
--- a/src/HashMap.php
+++ b/src/HashMap.php
@@ -7,16 +7,15 @@ namespace DNW\Skills;
  */
 class HashMap
 {
-    private $_hashToValue = [];
+    private array $_hashToValue = [];
 
-    private $_hashToKey = [];
+    private array $_hashToKey = [];
 
     public function getValue($key)
     {
         $hash = self::getHash($key);
-        $hashValue = $this->_hashToValue[$hash];
 
-        return $hashValue;
+        return $this->_hashToValue[$hash];
     }
 
     public function setValue($key, $value)
@@ -30,16 +29,12 @@ class HashMap
 
     public function getAllKeys()
     {
-        $keys = array_values($this->_hashToKey);
-
-        return $keys;
+        return array_values($this->_hashToKey);
     }
 
     public function getAllValues()
     {
-        $values = array_values($this->_hashToValue);
-
-        return $values;
+        return array_values($this->_hashToValue);
     }
 
     public function count()
diff --git a/src/Numerics/DiagonalMatrix.php b/src/Numerics/DiagonalMatrix.php
index 851b7e1..1af912d 100644
--- a/src/Numerics/DiagonalMatrix.php
+++ b/src/Numerics/DiagonalMatrix.php
@@ -14,7 +14,7 @@ class DiagonalMatrix extends Matrix
 
         for ($currentRow = 0; $currentRow < $rowCount; $currentRow++) {
             for ($currentCol = 0; $currentCol < $colCount; $currentCol++) {
-                if ($currentRow == $currentCol) {
+                if ($currentRow === $currentCol) {
                     $this->setValue($currentRow, $currentCol, $diagonalValues[$currentRow]);
                 } else {
                     $this->setValue($currentRow, $currentCol, 0);
diff --git a/src/Numerics/GaussianDistribution.php b/src/Numerics/GaussianDistribution.php
index 8a54f5e..8983088 100644
--- a/src/Numerics/GaussianDistribution.php
+++ b/src/Numerics/GaussianDistribution.php
@@ -8,12 +8,8 @@ namespace DNW\Skills\Numerics;
  * @author     Jeff Moser <jeff@moserware.com>
  * @copyright  2010 Jeff Moser
  */
-class GaussianDistribution
+class GaussianDistribution implements \Stringable
 {
-    private $_mean;
-
-    private $_standardDeviation;
-
     // precision and precisionMean are used because they make multiplying and dividing simpler
     // (the the accompanying math paper for more details)
     private $_precision;
@@ -22,11 +18,9 @@ class GaussianDistribution
 
     private $_variance;
 
-    public function __construct($mean = 0.0, $standardDeviation = 1.0)
+    public function __construct(private $_mean = 0.0, private $_standardDeviation = 1.0)
     {
-        $this->_mean = $mean;
-        $this->_standardDeviation = $standardDeviation;
-        $this->_variance = BasicMath::square($standardDeviation);
+        $this->_variance = BasicMath::square($_standardDeviation);
 
         if ($this->_variance != 0) {
             $this->_precision = 1.0 / $this->_variance;
@@ -34,11 +28,7 @@ class GaussianDistribution
         } else {
             $this->_precision = \INF;
 
-            if ($this->_mean == 0) {
-                $this->_precisionMean = 0;
-            } else {
-                $this->_precisionMean = \INF;
-            }
+            $this->_precisionMean = $this->_mean == 0 ? 0 : \INF;
         }
     }
 
@@ -172,9 +162,8 @@ class GaussianDistribution
 
         $multiplier = 1.0 / ($standardDeviation * sqrt(2 * M_PI));
         $expPart = exp((-1.0 * BasicMath::square($x - $mean)) / (2 * BasicMath::square($standardDeviation)));
-        $result = $multiplier * $expPart;
 
-        return $result;
+        return $multiplier * $expPart;
     }
 
     public static function cumulativeTo($x, $mean = 0.0, $standardDeviation = 1.0)
@@ -267,7 +256,7 @@ class GaussianDistribution
         return $mean - sqrt(2) * $standardDeviation * GaussianDistribution::inverseErrorFunctionCumulativeTo(2 * $x);
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return sprintf('mean=%.4f standardDeviation=%.4f', $this->_mean, $this->_standardDeviation);
     }
diff --git a/src/Numerics/Matrix.php b/src/Numerics/Matrix.php
index 8d5800e..15ccda7 100644
--- a/src/Numerics/Matrix.php
+++ b/src/Numerics/Matrix.php
@@ -6,19 +6,10 @@ use Exception;
 
 class Matrix
 {
-    const ERROR_TOLERANCE = 0.0000000001;
+    public const ERROR_TOLERANCE = 0.0000000001;
 
-    private $_matrixRowData;
-
-    private $_rowCount;
-
-    private $_columnCount;
-
-    public function __construct($rows = 0, $columns = 0, $matrixData = null)
+    public function __construct(private $_rowCount = 0, private $_columnCount = 0, private $_matrixRowData = null)
     {
-        $this->_rowCount = $rows;
-        $this->_columnCount = $columns;
-        $this->_matrixRowData = $matrixData;
     }
 
     public static function fromColumnValues($rows, $columns, $columnValues)
@@ -37,9 +28,8 @@ class Matrix
         return $result;
     }
 
-    public static function fromRowsColumns()
+    public static function fromRowsColumns(...$args)
     {
-        $args = \func_get_args();
         $rows = $args[0];
         $cols = $args[1];
         $result = new Matrix($rows, $cols);
@@ -138,7 +128,7 @@ class Matrix
             $firstRowColValue = $this->_matrixRowData[0][$currentColumn];
             $cofactor = $this->getCofactor(0, $currentColumn);
             $itemToAdd = $firstRowColValue * $cofactor;
-            $result = $result + $itemToAdd;
+            $result += $itemToAdd;
         }
 
         return $result;
@@ -258,7 +248,7 @@ class Matrix
                     $leftValue = $left->getValue($currentRow, $vectorIndex);
                     $rightValue = $right->getValue($vectorIndex, $currentColumn);
                     $vectorIndexProduct = $leftValue * $rightValue;
-                    $productValue = $productValue + $vectorIndexProduct;
+                    $productValue += $vectorIndexProduct;
                 }
 
                 $resultMatrix[$currentRow][$currentColumn] = $productValue;
diff --git a/src/Numerics/SquareMatrix.php b/src/Numerics/SquareMatrix.php
index 3592c2c..25b371d 100644
--- a/src/Numerics/SquareMatrix.php
+++ b/src/Numerics/SquareMatrix.php
@@ -4,9 +4,8 @@ namespace DNW\Skills\Numerics;
 
 class SquareMatrix extends Matrix
 {
-    public function __construct()
+    public function __construct(...$allValues)
     {
-        $allValues = func_get_args();
         $rows = (int) sqrt(count($allValues));
         $cols = $rows;
 
diff --git a/src/PairwiseComparison.php b/src/PairwiseComparison.php
index ddaf927..bf1738e 100644
--- a/src/PairwiseComparison.php
+++ b/src/PairwiseComparison.php
@@ -9,21 +9,18 @@ namespace DNW\Skills;
  */
 class PairwiseComparison
 {
-    const WIN = 1;
+    final const WIN = 1;
 
-    const DRAW = 0;
+    final const DRAW = 0;
 
-    const LOSE = -1;
+    final const LOSE = -1;
 
     public static function getRankFromComparison($comparison)
     {
-        switch ($comparison) {
-            case PairwiseComparison::WIN:
-                return [1, 2];
-            case PairwiseComparison::LOSE:
-                return [2, 1];
-            default:
-                return [1, 1];
-        }
+        return match ($comparison) {
+            PairwiseComparison::WIN => [1, 2],
+            PairwiseComparison::LOSE => [2, 1],
+            default => [1, 1],
+        };
     }
 }
diff --git a/src/Player.php b/src/Player.php
index 8161330..809f3b5 100644
--- a/src/Player.php
+++ b/src/Player.php
@@ -5,13 +5,11 @@ namespace DNW\Skills;
 /**
  * Represents a player who has a Rating.
  */
-class Player implements ISupportPartialPlay, ISupportPartialUpdate
+class Player implements ISupportPartialPlay, ISupportPartialUpdate, \Stringable
 {
-    const DEFAULT_PARTIAL_PLAY_PERCENTAGE = 1.0; // = 100% play time
+    final const DEFAULT_PARTIAL_PLAY_PERCENTAGE = 1.0; // = 100% play time
 
-    const DEFAULT_PARTIAL_UPDATE_PERCENTAGE = 1.0; // = receive 100% update
-
-    private $_Id;
+    final const DEFAULT_PARTIAL_UPDATE_PERCENTAGE = 1.0;
 
     private $_PartialPlayPercentage;
 
@@ -20,18 +18,17 @@ class Player implements ISupportPartialPlay, ISupportPartialUpdate
     /**
      * Constructs a player.
      *
-     * @param  mixed  $id The identifier for the player, such as a name.
+     * @param mixed $_Id The identifier for the player, such as a name.
      * @param  number  $partialPlayPercentage The weight percentage to give this player when calculating a new rank.
      * @param  number  $partialUpdatePercentage Indicated how much of a skill update a player should receive where 0 represents no update and 1.0 represents 100% of the update.
      */
-    public function __construct($id,
+    public function __construct(private $_Id,
                                 $partialPlayPercentage = self::DEFAULT_PARTIAL_PLAY_PERCENTAGE,
                                 $partialUpdatePercentage = self::DEFAULT_PARTIAL_UPDATE_PERCENTAGE)
     {
         // If they don't want to give a player an id, that's ok...
         Guard::argumentInRangeInclusive($partialPlayPercentage, 0.0, 1.0, 'partialPlayPercentage');
         Guard::argumentInRangeInclusive($partialUpdatePercentage, 0, 1.0, 'partialUpdatePercentage');
-        $this->_Id = $id;
         $this->_PartialPlayPercentage = $partialPlayPercentage;
         $this->_PartialUpdatePercentage = $partialUpdatePercentage;
     }
@@ -60,7 +57,7 @@ class Player implements ISupportPartialPlay, ISupportPartialUpdate
         return $this->_PartialUpdatePercentage;
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return (string) $this->_Id;
     }
diff --git a/src/PlayersRange.php b/src/PlayersRange.php
index f456888..c1d9949 100644
--- a/src/PlayersRange.php
+++ b/src/PlayersRange.php
@@ -6,11 +6,6 @@ use DNW\Skills\Numerics\Range;
 
 class PlayersRange extends Range
 {
-    public function __construct($min, $max)
-    {
-        parent::__construct($min, $max);
-    }
-
     protected static function create($min, $max)
     {
         return new PlayersRange($min, $max);
diff --git a/src/Rating.php b/src/Rating.php
index 6732836..e7d79f8 100644
--- a/src/Rating.php
+++ b/src/Rating.php
@@ -5,28 +5,19 @@ namespace DNW\Skills;
 // Container for a player's rating.
 use DNW\Skills\Numerics\GaussianDistribution;
 
-class Rating
+class Rating implements \Stringable
 {
-    const CONSERVATIVE_STANDARD_DEVIATION_MULTIPLIER = 3;
-
-    private $_conservativeStandardDeviationMultiplier;
-
-    private $_mean;
-
-    private $_standardDeviation;
+    final const CONSERVATIVE_STANDARD_DEVIATION_MULTIPLIER = 3;
 
     /**
      * Constructs a rating.
      *
-     * @param  float  $mean The statistical mean value of the rating (also known as mu).
-     * @param  float  $standardDeviation The standard deviation of the rating (also known as s).
-     * @param  float|int  $conservativeStandardDeviationMultiplier optional The number of standardDeviations to subtract from the mean to achieve a conservative rating.
+     * @param float $_mean The statistical mean value of the rating (also known as mu).
+     * @param float $_standardDeviation The standard deviation of the rating (also known as s).
+     * @param float|int $_conservativeStandardDeviationMultiplier optional The number of standardDeviations to subtract from the mean to achieve a conservative rating.
      */
-    public function __construct($mean, $standardDeviation, $conservativeStandardDeviationMultiplier = self::CONSERVATIVE_STANDARD_DEVIATION_MULTIPLIER)
+    public function __construct(private $_mean, private $_standardDeviation, private $_conservativeStandardDeviationMultiplier = self::CONSERVATIVE_STANDARD_DEVIATION_MULTIPLIER)
     {
-        $this->_mean = $mean;
-        $this->_standardDeviation = $standardDeviation;
-        $this->_conservativeStandardDeviationMultiplier = $conservativeStandardDeviationMultiplier;
     }
 
     /**
@@ -76,7 +67,7 @@ class Rating
         return new Rating($partialPosteriorGaussion->getMean(), $partialPosteriorGaussion->getStandardDeviation(), $prior->_conservativeStandardDeviationMultiplier);
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return sprintf('mean=%.4f, standardDeviation=%.4f', $this->_mean, $this->_standardDeviation);
     }
diff --git a/src/SkillCalculator.php b/src/SkillCalculator.php
index 48656ba..4f07716 100644
--- a/src/SkillCalculator.php
+++ b/src/SkillCalculator.php
@@ -9,17 +9,8 @@ use Exception;
  */
 abstract class SkillCalculator
 {
-    private $_supportedOptions;
-
-    private $_playersPerTeamAllowed;
-
-    private $_totalTeamsAllowed;
-
-    protected function __construct($supportedOptions, TeamsRange $totalTeamsAllowed, PlayersRange $playerPerTeamAllowed)
+    protected function __construct(private $_supportedOptions, private readonly TeamsRange $_totalTeamsAllowed, private readonly PlayersRange $_playersPerTeamAllowed)
     {
-        $this->_supportedOptions = $supportedOptions;
-        $this->_totalTeamsAllowed = $totalTeamsAllowed;
-        $this->_playersPerTeamAllowed = $playerPerTeamAllowed;
     }
 
     /**
@@ -55,8 +46,6 @@ abstract class SkillCalculator
 
     /**
      * @param  array<\DNW\Skills\Team>  $teams
-     * @param  \DNW\Skills\TeamsRange  $totalTeams
-     * @param  \DNW\Skills\PlayersRange  $playersPerTeam
      * @return void
      * @throws \Exception
      */
@@ -79,9 +68,9 @@ abstract class SkillCalculator
 
 class SkillCalculatorSupportedOptions
 {
-    const NONE = 0x00;
+    final const NONE = 0x00;
 
-    const PARTIAL_PLAY = 0x01;
+    final const PARTIAL_PLAY = 0x01;
 
-    const PARTIAL_UPDATE = 0x02;
+    final const PARTIAL_UPDATE = 0x02;
 }
diff --git a/src/Teams.php b/src/Teams.php
index 8c1e89f..ab88dec 100644
--- a/src/Teams.php
+++ b/src/Teams.php
@@ -4,9 +4,8 @@ namespace DNW\Skills;
 
 class Teams
 {
-    public static function concat(/*variable arguments*/)
+    public static function concat(...$args/*variable arguments*/)
     {
-        $args = func_get_args();
         $result = [];
 
         foreach ($args as $currentTeam) {
diff --git a/src/TeamsRange.php b/src/TeamsRange.php
index 7fe358f..d35b8a9 100644
--- a/src/TeamsRange.php
+++ b/src/TeamsRange.php
@@ -6,11 +6,6 @@ use DNW\Skills\Numerics\Range;
 
 class TeamsRange extends Range
 {
-    public function __construct($min, $max)
-    {
-        parent::__construct($min, $max);
-    }
-
     protected static function create($min, $max)
     {
         return new TeamsRange($min, $max);
diff --git a/src/TrueSkill/FactorGraphTrueSkillCalculator.php b/src/TrueSkill/FactorGraphTrueSkillCalculator.php
index 094af35..60fc999 100644
--- a/src/TrueSkill/FactorGraphTrueSkillCalculator.php
+++ b/src/TrueSkill/FactorGraphTrueSkillCalculator.php
@@ -38,7 +38,7 @@ class FactorGraphTrueSkillCalculator extends SkillCalculator
         $factorGraph->buildGraph();
         $factorGraph->runSchedule();
 
-        $probabilityOfOutcome = $factorGraph->getProbabilityOfRanking();
+        $factorGraph->getProbabilityOfRanking();
 
         return $factorGraph->getUpdatedRatings();
     }
@@ -47,11 +47,11 @@ class FactorGraphTrueSkillCalculator extends SkillCalculator
     {
         // We need to create the A matrix which is the player team assigments.
         $teamAssignmentsList = $teams;
-        $skillsMatrix = $this->getPlayerCovarianceMatrix($teamAssignmentsList);
-        $meanVector = $this->getPlayerMeansVector($teamAssignmentsList);
+        $skillsMatrix = self::getPlayerCovarianceMatrix($teamAssignmentsList);
+        $meanVector = self::getPlayerMeansVector($teamAssignmentsList);
         $meanVectorTranspose = $meanVector->getTranspose();
 
-        $playerTeamAssignmentsMatrix = $this->createPlayerTeamAssignmentMatrix($teamAssignmentsList, $meanVector->getRowCount());
+        $playerTeamAssignmentsMatrix = self::createPlayerTeamAssignmentMatrix($teamAssignmentsList, $meanVector->getRowCount());
         $playerTeamAssignmentsMatrixTranspose = $playerTeamAssignmentsMatrix->getTranspose();
 
         $betaSquared = BasicMath::square($gameInfo->getBeta());
@@ -81,18 +81,14 @@ class FactorGraphTrueSkillCalculator extends SkillCalculator
         $sqrtPartDenominator = $middle->getDeterminant();
         $sqrtPart = $sqrtPartNumerator / $sqrtPartDenominator;
 
-        $result = exp($expPart) * sqrt($sqrtPart);
-
-        return $result;
+        return exp($expPart) * sqrt($sqrtPart);
     }
 
     private static function getPlayerMeansVector(array $teamAssignmentsList)
     {
         // A simple vector of all the player means.
         return new Vector(self::getPlayerRatingValues($teamAssignmentsList,
-            function ($rating) {
-                return $rating->getMean();
-            }));
+            fn($rating) => $rating->getMean()));
     }
 
     private static function getPlayerCovarianceMatrix(array $teamAssignmentsList)
@@ -101,9 +97,7 @@ class FactorGraphTrueSkillCalculator extends SkillCalculator
         // players.
         return new DiagonalMatrix(
             self::getPlayerRatingValues($teamAssignmentsList,
-                function ($rating) {
-                    return BasicMath::square($rating->getStandardDeviation());
-                }));
+                fn($rating) => BasicMath::square($rating->getStandardDeviation())));
     }
 
     // Helper function that gets a list of values for all player ratings
@@ -141,7 +135,7 @@ class FactorGraphTrueSkillCalculator extends SkillCalculator
         $playerAssignments = [];
         $totalPreviousPlayers = 0;
 
-        $teamAssignmentsListCount = count($teamAssignmentsList);
+        $teamAssignmentsListCount = is_countable($teamAssignmentsList) ? count($teamAssignmentsList) : 0;
 
         $currentColumn = 0;
 
@@ -175,8 +169,6 @@ class FactorGraphTrueSkillCalculator extends SkillCalculator
             $currentColumn++;
         }
 
-        $playerTeamAssignmentsMatrix = Matrix::fromColumnValues($totalPlayers, $teamAssignmentsListCount - 1, $playerAssignments);
-
-        return $playerTeamAssignmentsMatrix;
+        return Matrix::fromColumnValues($totalPlayers, $teamAssignmentsListCount - 1, $playerAssignments);
     }
 }
diff --git a/src/TrueSkill/Factors/GaussianFactor.php b/src/TrueSkill/Factors/GaussianFactor.php
index 3663878..82dd312 100644
--- a/src/TrueSkill/Factors/GaussianFactor.php
+++ b/src/TrueSkill/Factors/GaussianFactor.php
@@ -9,19 +9,10 @@ use DNW\Skills\Numerics\GaussianDistribution;
 
 abstract class GaussianFactor extends Factor
 {
-    protected function __construct($name)
-    {
-        parent::__construct($name);
-    }
-
     /**
      * Sends the factor-graph message with and returns the log-normalization constant.
-     *
-     * @param  Message  $message
-     * @param  Variable  $variable
-     * @return float|int
      */
-    protected function sendMessageVariable(Message $message, Variable $variable)
+    protected function sendMessageVariable(Message $message, Variable $variable): float|int
     {
         $marginal = $variable->getValue();
         $messageValue = $message->getValue();
@@ -34,11 +25,10 @@ abstract class GaussianFactor extends Factor
     public function createVariableToMessageBinding(Variable $variable)
     {
         $newDistribution = GaussianDistribution::fromPrecisionMean(0, 0);
-        $binding = parent::createVariableToMessageBindingWithMessage($variable,
+
+        return parent::createVariableToMessageBindingWithMessage($variable,
             new Message(
                 $newDistribution,
                 sprintf('message from %s to %s', $this, $variable)));
-
-        return $binding;
     }
 }
diff --git a/src/TrueSkill/Factors/GaussianLikelihoodFactor.php b/src/TrueSkill/Factors/GaussianLikelihoodFactor.php
index 6319c29..47d483d 100644
--- a/src/TrueSkill/Factors/GaussianLikelihoodFactor.php
+++ b/src/TrueSkill/Factors/GaussianLikelihoodFactor.php
@@ -71,15 +71,12 @@ class GaussianLikelihoodFactor extends GaussianFactor
         $messages = $this->getMessages();
         $vars = $this->getVariables();
 
-        switch ($messageIndex) {
-            case 0:
-                return $this->updateHelper($messages[0], $messages[1],
-                    $vars[0], $vars[1]);
-            case 1:
-                return $this->updateHelper($messages[1], $messages[0],
-                    $vars[1], $vars[0]);
-            default:
-                throw new Exception();
-        }
+        return match ($messageIndex) {
+            0 => $this->updateHelper($messages[0], $messages[1],
+                $vars[0], $vars[1]),
+            1 => $this->updateHelper($messages[1], $messages[0],
+                $vars[1], $vars[0]),
+            default => throw new Exception(),
+        };
     }
 }
diff --git a/src/TrueSkill/Factors/GaussianPriorFactor.php b/src/TrueSkill/Factors/GaussianPriorFactor.php
index c026041..e3b34fd 100644
--- a/src/TrueSkill/Factors/GaussianPriorFactor.php
+++ b/src/TrueSkill/Factors/GaussianPriorFactor.php
@@ -38,5 +38,6 @@ class GaussianPriorFactor extends GaussianFactor
         $message->setValue($this->_newMessage);
 
         return GaussianDistribution::subtract($oldMarginal, $newMarginal);
+
     }
 }
diff --git a/src/TrueSkill/Factors/GaussianWeightedSumFactor.php b/src/TrueSkill/Factors/GaussianWeightedSumFactor.php
index b612ec8..4527d78 100644
--- a/src/TrueSkill/Factors/GaussianWeightedSumFactor.php
+++ b/src/TrueSkill/Factors/GaussianWeightedSumFactor.php
@@ -15,24 +15,22 @@ use DNW\Skills\Numerics\GaussianDistribution;
  */
 class GaussianWeightedSumFactor extends GaussianFactor
 {
-    private $_variableIndexOrdersForWeights = [];
+    private array $_variableIndexOrdersForWeights = [];
 
     // This following is used for convenience, for example, the first entry is [0, 1, 2]
     // corresponding to v[0] = a1*v[1] + a2*v[2]
-    private $_weights;
+    private array $_weights = [];
 
-    private $_weightsSquared;
+    private array $_weightsSquared = [];
 
     public function __construct(Variable $sumVariable, array $variablesToSum, array $variableWeights = null)
     {
         parent::__construct(self::createName($sumVariable, $variablesToSum, $variableWeights));
-        $this->_weights = [];
-        $this->_weightsSquared = [];
 
         // The first weights are a straightforward copy
         // v_0 = a_1*v_1 + a_2*v_2 + ... + a_n * v_n
-        $variableWeightsLength = count($variableWeights);
-        $this->_weights[0] = array_fill(0, count($variableWeights), 0);
+        $variableWeightsLength = count((array) $variableWeights);
+        $this->_weights[0] = array_fill(0, count((array) $variableWeights), 0);
 
         for ($i = 0; $i < $variableWeightsLength; $i++) {
             $weight = &$variableWeights[$i];
@@ -48,7 +46,7 @@ class GaussianWeightedSumFactor extends GaussianFactor
             $this->_variableIndexOrdersForWeights[0][] = $i;
         }
 
-        $variableWeightsLength = count($variableWeights);
+        $variableWeightsLength = count((array) $variableWeights);
 
         // The rest move the variables around and divide out the constant.
         // For example:
@@ -71,7 +69,7 @@ class GaussianWeightedSumFactor extends GaussianFactor
             for ($currentWeightSourceIndex = 0;
                  $currentWeightSourceIndex < $variableWeightsLength;
                  $currentWeightSourceIndex++) {
-                if ($currentWeightSourceIndex == ($weightsIndex - 1)) {
+                if ($currentWeightSourceIndex === $weightsIndex - 1) {
                     continue;
                 }
 
@@ -98,7 +96,7 @@ class GaussianWeightedSumFactor extends GaussianFactor
             }
             $currentWeights[$currentDestinationWeightIndex] = $finalWeight;
             $currentWeightsSquared[$currentDestinationWeightIndex] = BasicMath::square($finalWeight);
-            $variableIndices[count($variableWeights)] = 0;
+            $variableIndices[count((array) $variableWeights)] = 0;
             $this->_variableIndexOrdersForWeights[] = $variableIndices;
 
             $this->_weights[$weightsIndex] = $currentWeights;
@@ -121,7 +119,7 @@ class GaussianWeightedSumFactor extends GaussianFactor
         $result = 0.0;
 
         // We start at 1 since offset 0 has the sum
-        $varCount = count($vars);
+        $varCount = is_countable($vars) ? count($vars) : 0;
         for ($i = 1; $i < $varCount; $i++) {
             $result += GaussianDistribution::logRatioNormalization($vars[$i]->getValue(), $messages[$i]->getValue());
         }
@@ -167,7 +165,6 @@ class GaussianWeightedSumFactor extends GaussianFactor
         $anotherNewPrecision = 1.0 / $anotherInverseOfNewPrecisionSum;
 
         $newPrecisionMean = $newPrecision * $weightedMeanSum;
-        $anotherNewPrecisionMean = $anotherNewPrecision * $anotherWeightedMeanSum;
 
         $newMessage = GaussianDistribution::fromPrecisionMean($newPrecisionMean, $newPrecision);
         $oldMarginalWithoutMessage = GaussianDistribution::divide($marginal0, $message0);
@@ -190,7 +187,7 @@ class GaussianWeightedSumFactor extends GaussianFactor
         $allMessages = $this->getMessages();
         $allVariables = $this->getVariables();
 
-        Guard::argumentIsValidIndex($messageIndex, count($allMessages), 'messageIndex');
+        Guard::argumentIsValidIndex($messageIndex, is_countable($allMessages) ? count($allMessages) : 0, 'messageIndex');
 
         $updatedMessages = [];
         $updatedVariables = [];
@@ -200,7 +197,7 @@ class GaussianWeightedSumFactor extends GaussianFactor
         // The tricky part here is that we have to put the messages and variables in the same
         // order as the weights. Thankfully, the weights and messages share the same index numbers,
         // so we just need to make sure they're consistent
-        $allMessagesCount = count($allMessages);
+        $allMessagesCount = is_countable($allMessages) ? count($allMessages) : 0;
         for ($i = 0; $i < $allMessagesCount; $i++) {
             $updatedMessages[] = $allMessages[$indicesToUse[$i]];
             $updatedVariables[] = $allVariables[$indicesToUse[$i]];
@@ -218,7 +215,7 @@ class GaussianWeightedSumFactor extends GaussianFactor
         $result = (string) $sumVariable;
         $result .= ' = ';
 
-        $totalVars = count($variablesToSum);
+        $totalVars = is_countable($variablesToSum) ? count($variablesToSum) : 0;
         for ($i = 0; $i < $totalVars; $i++) {
             $isFirst = ($i == 0);
 
@@ -232,7 +229,7 @@ class GaussianWeightedSumFactor extends GaussianFactor
             $result .= (string) $variablesToSum[$i];
             $result .= ']';
 
-            $isLast = ($i == ($totalVars - 1));
+            $isLast = ($i === $totalVars - 1);
 
             if (! $isLast) {
                 if ($weights[$i + 1] >= 0) {
diff --git a/src/TrueSkill/Layers/IteratedTeamDifferencesInnerLayer.php b/src/TrueSkill/Layers/IteratedTeamDifferencesInnerLayer.php
index c6d9318..f99afc9 100644
--- a/src/TrueSkill/Layers/IteratedTeamDifferencesInnerLayer.php
+++ b/src/TrueSkill/Layers/IteratedTeamDifferencesInnerLayer.php
@@ -11,26 +11,18 @@ use Exception;
 // The whole purpose of this is to do a loop on the bottom
 class IteratedTeamDifferencesInnerLayer extends TrueSkillFactorGraphLayer
 {
-    private $_TeamDifferencesComparisonLayer;
-
-    private $_TeamPerformancesToTeamPerformanceDifferencesLayer;
-
     public function __construct(TrueSkillFactorGraph $parentGraph,
-                                TeamPerformancesToTeamPerformanceDifferencesLayer $teamPerformancesToPerformanceDifferences,
-                                TeamDifferencesComparisonLayer $teamDifferencesComparisonLayer)
+                                private readonly TeamPerformancesToTeamPerformanceDifferencesLayer $_TeamPerformancesToTeamPerformanceDifferencesLayer,
+                                private readonly TeamDifferencesComparisonLayer $_TeamDifferencesComparisonLayer)
     {
         parent::__construct($parentGraph);
-        $this->_TeamPerformancesToTeamPerformanceDifferencesLayer = $teamPerformancesToPerformanceDifferences;
-        $this->_TeamDifferencesComparisonLayer = $teamDifferencesComparisonLayer;
     }
 
     public function getLocalFactors()
     {
-        $localFactors = array_merge($this->_TeamPerformancesToTeamPerformanceDifferencesLayer->getLocalFactors(),
+        return array_merge($this->_TeamPerformancesToTeamPerformanceDifferencesLayer->getLocalFactors(),
             $this->_TeamDifferencesComparisonLayer->getLocalFactors()
         );
-
-        return $localFactors;
     }
 
     public function buildLayer()
@@ -46,7 +38,7 @@ class IteratedTeamDifferencesInnerLayer extends TrueSkillFactorGraphLayer
 
     public function createPriorSchedule()
     {
-        switch (count($this->getInputVariablesGroups())) {
+        switch (is_countable($this->getInputVariablesGroups()) ? count($this->getInputVariablesGroups()) : 0) {
             case 0:
             case 1:
                 throw new Exception('InvalidOperation');
@@ -59,15 +51,14 @@ class IteratedTeamDifferencesInnerLayer extends TrueSkillFactorGraphLayer
         }
 
         // When dealing with differences, there are always (n-1) differences, so add in the 1
-        $totalTeamDifferences = count($this->_TeamPerformancesToTeamPerformanceDifferencesLayer->getLocalFactors());
-        $totalTeams = $totalTeamDifferences + 1;
+        $totalTeamDifferences = is_countable($this->_TeamPerformancesToTeamPerformanceDifferencesLayer->getLocalFactors()) ? count($this->_TeamPerformancesToTeamPerformanceDifferencesLayer->getLocalFactors()) : 0;
 
         $localFactors = $this->_TeamPerformancesToTeamPerformanceDifferencesLayer->getLocalFactors();
 
         $firstDifferencesFactor = $localFactors[0];
         $lastDifferencesFactor = $localFactors[$totalTeamDifferences - 1];
 
-        $innerSchedule = new ScheduleSequence(
+        return new ScheduleSequence(
             'inner schedule',
             [
                 $loop,
@@ -79,8 +70,6 @@ class IteratedTeamDifferencesInnerLayer extends TrueSkillFactorGraphLayer
                     $lastDifferencesFactor, 2),
             ]
         );
-
-        return $innerSchedule;
     }
 
     private function createTwoTeamInnerPriorLoopSchedule()
@@ -108,7 +97,7 @@ class IteratedTeamDifferencesInnerLayer extends TrueSkillFactorGraphLayer
 
     private function createMultipleTeamInnerPriorLoopSchedule()
     {
-        $totalTeamDifferences = count($this->_TeamPerformancesToTeamPerformanceDifferencesLayer->getLocalFactors());
+        $totalTeamDifferences = is_countable($this->_TeamPerformancesToTeamPerformanceDifferencesLayer->getLocalFactors()) ? count($this->_TeamPerformancesToTeamPerformanceDifferencesLayer->getLocalFactors()) : 0;
 
         $forwardScheduleList = [];
 
@@ -173,11 +162,9 @@ class IteratedTeamDifferencesInnerLayer extends TrueSkillFactorGraphLayer
 
         $initialMaxDelta = 0.0001;
 
-        $loop = new ScheduleLoop(
+        return new ScheduleLoop(
             sprintf('loop with max delta of %f', $initialMaxDelta),
             $forwardBackwardScheduleToLoop,
             $initialMaxDelta);
-
-        return $loop;
     }
 }
diff --git a/src/TrueSkill/Layers/PlayerPerformancesToTeamPerformancesLayer.php b/src/TrueSkill/Layers/PlayerPerformancesToTeamPerformancesLayer.php
index ac33f21..fe859d3 100644
--- a/src/TrueSkill/Layers/PlayerPerformancesToTeamPerformancesLayer.php
+++ b/src/TrueSkill/Layers/PlayerPerformancesToTeamPerformancesLayer.php
@@ -9,11 +9,6 @@ use DNW\Skills\TrueSkill\TrueSkillFactorGraph;
 
 class PlayerPerformancesToTeamPerformancesLayer extends TrueSkillFactorGraphLayer
 {
-    public function __construct(TrueSkillFactorGraph $parentGraph)
-    {
-        parent::__construct($parentGraph);
-    }
-
     public function buildLayer()
     {
         $inputVariablesGroups = $this->getInputVariablesGroups();
@@ -34,15 +29,11 @@ class PlayerPerformancesToTeamPerformancesLayer extends TrueSkillFactorGraphLaye
     {
         $localFactors = $this->getLocalFactors();
 
-        $sequence = $this->scheduleSequence(
+        return $this->scheduleSequence(
             array_map(
-                function ($weightedSumFactor) {
-                    return new ScheduleStep('Perf to Team Perf Step', $weightedSumFactor, 0);
-                },
+                fn($weightedSumFactor) => new ScheduleStep('Perf to Team Perf Step', $weightedSumFactor, 0),
                 $localFactors),
             'all player perf to team perf schedule');
-
-        return $sequence;
     }
 
     protected function createPlayerToTeamSumFactor($teamMembers, $sumVariable)
@@ -79,13 +70,10 @@ class PlayerPerformancesToTeamPerformancesLayer extends TrueSkillFactorGraphLaye
 
     private function createOutputVariable($team)
     {
-        $memberNames = array_map(function ($currentPlayer) {
-            return (string) ($currentPlayer->getKey());
-        }, $team);
+        $memberNames = array_map(fn($currentPlayer) => (string) ($currentPlayer->getKey()), $team);
 
         $teamMemberNames = \implode(', ', $memberNames);
-        $outputVariable = $this->getParentFactorGraph()->getVariableFactory()->createBasicVariable('Team['.$teamMemberNames."]'s performance");
 
-        return $outputVariable;
+        return $this->getParentFactorGraph()->getVariableFactory()->createBasicVariable('Team['.$teamMemberNames."]'s performance");
     }
 }
diff --git a/src/TrueSkill/Layers/PlayerPriorValuesToSkillsLayer.php b/src/TrueSkill/Layers/PlayerPriorValuesToSkillsLayer.php
index 20d10f5..8144b98 100644
--- a/src/TrueSkill/Layers/PlayerPriorValuesToSkillsLayer.php
+++ b/src/TrueSkill/Layers/PlayerPriorValuesToSkillsLayer.php
@@ -13,12 +13,9 @@ use DNW\Skills\TrueSkill\TrueSkillFactorGraph;
 // start the process.
 class PlayerPriorValuesToSkillsLayer extends TrueSkillFactorGraphLayer
 {
-    private $_teams;
-
-    public function __construct(TrueSkillFactorGraph $parentGraph, array $teams)
+    public function __construct(TrueSkillFactorGraph $parentGraph, private readonly array $_teams)
     {
         parent::__construct($parentGraph);
-        $this->_teams = $teams;
     }
 
     public function buildLayer()
@@ -33,7 +30,7 @@ class PlayerPriorValuesToSkillsLayer extends TrueSkillFactorGraphLayer
                 $localCurrentTeamPlayer = $currentTeamPlayer;
                 $currentTeamPlayerRating = $currentTeam->getRating($localCurrentTeamPlayer);
                 $playerSkill = $this->createSkillOutputVariable($localCurrentTeamPlayer);
-                $priorFactor = $this->createPriorFactor($localCurrentTeamPlayer, $currentTeamPlayerRating, $playerSkill);
+                $priorFactor = $this->createPriorFactor($currentTeamPlayerRating, $playerSkill);
                 $this->addLayerFactor($priorFactor);
                 $currentTeamSkills[] = $playerSkill;
             }
@@ -49,14 +46,12 @@ class PlayerPriorValuesToSkillsLayer extends TrueSkillFactorGraphLayer
 
         return $this->scheduleSequence(
             array_map(
-                function ($prior) {
-                    return new ScheduleStep('Prior to Skill Step', $prior, 0);
-                },
+                fn($prior) => new ScheduleStep('Prior to Skill Step', $prior, 0),
                 $localFactors),
             'All priors');
     }
 
-    private function createPriorFactor($player, Rating $priorRating, Variable $skillsVariable)
+    private function createPriorFactor(Rating $priorRating, Variable $skillsVariable)
     {
         return new GaussianPriorFactor(
             $priorRating->getMean(),
@@ -70,8 +65,7 @@ class PlayerPriorValuesToSkillsLayer extends TrueSkillFactorGraphLayer
     {
         $parentFactorGraph = $this->getParentFactorGraph();
         $variableFactory = $parentFactorGraph->getVariableFactory();
-        $skillOutputVariable = $variableFactory->createKeyedVariable($key, $key."'s skill");
 
-        return $skillOutputVariable;
+        return $variableFactory->createKeyedVariable($key, $key."'s skill");
     }
 }
diff --git a/src/TrueSkill/Layers/PlayerSkillsToPerformancesLayer.php b/src/TrueSkill/Layers/PlayerSkillsToPerformancesLayer.php
index 104f593..33d1332 100644
--- a/src/TrueSkill/Layers/PlayerSkillsToPerformancesLayer.php
+++ b/src/TrueSkill/Layers/PlayerSkillsToPerformancesLayer.php
@@ -10,11 +10,6 @@ use DNW\Skills\TrueSkill\TrueSkillFactorGraph;
 
 class PlayerSkillsToPerformancesLayer extends TrueSkillFactorGraphLayer
 {
-    public function __construct(TrueSkillFactorGraph $parentGraph)
-    {
-        parent::__construct($parentGraph);
-    }
-
     public function buildLayer()
     {
         $inputVariablesGroups = $this->getInputVariablesGroups();
@@ -47,9 +42,7 @@ class PlayerSkillsToPerformancesLayer extends TrueSkillFactorGraphLayer
 
     private function createOutputVariable($key)
     {
-        $outputVariable = $this->getParentFactorGraph()->getVariableFactory()->createKeyedVariable($key, $key."'s performance");
-
-        return $outputVariable;
+        return $this->getParentFactorGraph()->getVariableFactory()->createKeyedVariable($key, $key."'s performance");
     }
 
     public function createPriorSchedule()
@@ -58,9 +51,7 @@ class PlayerSkillsToPerformancesLayer extends TrueSkillFactorGraphLayer
 
         return $this->scheduleSequence(
             array_map(
-                function ($likelihood) {
-                    return new ScheduleStep('Skill to Perf step', $likelihood, 0);
-                },
+                fn($likelihood) => new ScheduleStep('Skill to Perf step', $likelihood, 0),
                 $localFactors),
             'All skill to performance sending');
     }
@@ -71,9 +62,7 @@ class PlayerSkillsToPerformancesLayer extends TrueSkillFactorGraphLayer
 
         return $this->scheduleSequence(
             array_map(
-                function ($likelihood) {
-                    return new ScheduleStep('name', $likelihood, 1);
-                },
+                fn($likelihood) => new ScheduleStep('name', $likelihood, 1),
                 $localFactors),
             'All skill to performance sending');
     }
diff --git a/src/TrueSkill/Layers/TeamDifferencesComparisonLayer.php b/src/TrueSkill/Layers/TeamDifferencesComparisonLayer.php
index ccd00cc..efda551 100644
--- a/src/TrueSkill/Layers/TeamDifferencesComparisonLayer.php
+++ b/src/TrueSkill/Layers/TeamDifferencesComparisonLayer.php
@@ -11,12 +11,9 @@ class TeamDifferencesComparisonLayer extends TrueSkillFactorGraphLayer
 {
     private $_epsilon;
 
-    private $_teamRanks;
-
-    public function __construct(TrueSkillFactorGraph $parentGraph, array $teamRanks)
+    public function __construct(TrueSkillFactorGraph $parentGraph, private readonly array $_teamRanks)
     {
         parent::__construct($parentGraph);
-        $this->_teamRanks = $teamRanks;
         $gameInfo = $this->getParentFactorGraph()->getGameInfo();
         $this->_epsilon = DrawMargin::getDrawMarginFromDrawProbability($gameInfo->getDrawProbability(), $gameInfo->getBeta());
     }
@@ -24,7 +21,7 @@ class TeamDifferencesComparisonLayer extends TrueSkillFactorGraphLayer
     public function buildLayer()
     {
         $inputVarGroups = $this->getInputVariablesGroups();
-        $inputVarGroupsCount = count($inputVarGroups);
+        $inputVarGroupsCount = is_countable($inputVarGroups) ? count($inputVarGroups) : 0;
 
         for ($i = 0; $i < $inputVarGroupsCount; $i++) {
             $isDraw = ($this->_teamRanks[$i] == $this->_teamRanks[$i + 1]);
diff --git a/src/TrueSkill/Layers/TeamPerformancesToTeamPerformanceDifferencesLayer.php b/src/TrueSkill/Layers/TeamPerformancesToTeamPerformanceDifferencesLayer.php
index 3f06af6..f762ee0 100644
--- a/src/TrueSkill/Layers/TeamPerformancesToTeamPerformanceDifferencesLayer.php
+++ b/src/TrueSkill/Layers/TeamPerformancesToTeamPerformanceDifferencesLayer.php
@@ -8,15 +8,10 @@ use DNW\Skills\TrueSkill\TrueSkillFactorGraph;
 
 class TeamPerformancesToTeamPerformanceDifferencesLayer extends TrueSkillFactorGraphLayer
 {
-    public function __construct(TrueSkillFactorGraph $parentGraph)
-    {
-        parent::__construct($parentGraph);
-    }
-
     public function buildLayer()
     {
         $inputVariablesGroups = $this->getInputVariablesGroups();
-        $inputVariablesGroupsCount = count($inputVariablesGroups);
+        $inputVariablesGroupsCount = is_countable($inputVariablesGroups) ? count($inputVariablesGroups) : 0;
         $outputVariablesGroup = &$this->getOutputVariablesGroups();
 
         for ($i = 0; $i < $inputVariablesGroupsCount - 1; $i++) {
@@ -44,8 +39,6 @@ class TeamPerformancesToTeamPerformanceDifferencesLayer extends TrueSkillFactorG
 
     private function createOutputVariable()
     {
-        $outputVariable = $this->getParentFactorGraph()->getVariableFactory()->createBasicVariable('Team performance difference');
-
-        return $outputVariable;
+        return $this->getParentFactorGraph()->getVariableFactory()->createBasicVariable('Team performance difference');
     }
 }
diff --git a/src/TrueSkill/TrueSkillFactorGraph.php b/src/TrueSkill/TrueSkillFactorGraph.php
index b7a0735..6c1aff6 100644
--- a/src/TrueSkill/TrueSkillFactorGraph.php
+++ b/src/TrueSkill/TrueSkillFactorGraph.php
@@ -19,20 +19,15 @@ use DNW\Skills\TrueSkill\Layers\TeamPerformancesToTeamPerformanceDifferencesLaye
 
 class TrueSkillFactorGraph extends FactorGraph
 {
-    private $_gameInfo;
-
     private $_layers;
 
     private $_priorLayer;
 
-    public function __construct(GameInfo $gameInfo, array $teams, array $teamRanks)
+    public function __construct(private readonly GameInfo $_gameInfo, array $teams, array $teamRanks)
     {
         $this->_priorLayer = new PlayerPriorValuesToSkillsLayer($this, $teams);
-        $this->_gameInfo = $gameInfo;
         $newFactory = new VariableFactory(
-            function () {
-                return GaussianDistribution::fromPrecisionMean(0, 0);
-            });
+            fn() => GaussianDistribution::fromPrecisionMean(0, 0));
 
         $this->setVariableFactory($newFactory);
         $this->_layers = [
@@ -70,7 +65,7 @@ class TrueSkillFactorGraph extends FactorGraph
     public function runSchedule()
     {
         $fullSchedule = $this->createFullSchedule();
-        $fullScheduleDelta = $fullSchedule->visit();
+        $fullSchedule->visit();
     }
 
     public function getProbabilityOfRanking()
diff --git a/src/TrueSkill/TwoTeamTrueSkillCalculator.php b/src/TrueSkill/TwoTeamTrueSkillCalculator.php
index 106d4d1..2695778 100644
--- a/src/TrueSkill/TwoTeamTrueSkillCalculator.php
+++ b/src/TrueSkill/TwoTeamTrueSkillCalculator.php
@@ -72,16 +72,12 @@ class TwoTeamTrueSkillCalculator extends SkillCalculator
 
         $totalPlayers = $selfTeam->count() + $otherTeam->count();
 
-        $meanGetter = function ($currentRating) {
-            return $currentRating->getMean();
-        };
+        $meanGetter = fn($currentRating) => $currentRating->getMean();
 
         $selfMeanSum = BasicMath::sum($selfTeam->getAllRatings(), $meanGetter);
         $otherTeamMeanSum = BasicMath::sum($otherTeam->getAllRatings(), $meanGetter);
 
-        $varianceGetter = function ($currentRating) {
-            return BasicMath::square($currentRating->getStandardDeviation());
-        };
+        $varianceGetter = fn($currentRating) => BasicMath::square($currentRating->getStandardDeviation());
 
         $c = sqrt(
             BasicMath::sum($selfTeam->getAllRatings(), $varianceGetter)
@@ -148,22 +144,18 @@ class TwoTeamTrueSkillCalculator extends SkillCalculator
 
         // We've verified that there's just two teams
         $team1Ratings = $teams[0]->getAllRatings();
-        $team1Count = count($team1Ratings);
+        $team1Count = is_countable($team1Ratings) ? count($team1Ratings) : 0;
 
         $team2Ratings = $teams[1]->getAllRatings();
-        $team2Count = count($team2Ratings);
+        $team2Count = is_countable($team2Ratings) ? count($team2Ratings) : 0;
 
         $totalPlayers = $team1Count + $team2Count;
 
         $betaSquared = BasicMath::square($gameInfo->getBeta());
 
-        $meanGetter = function ($currentRating) {
-            return $currentRating->getMean();
-        };
+        $meanGetter = fn($currentRating) => $currentRating->getMean();
 
-        $varianceGetter = function ($currentRating) {
-            return BasicMath::square($currentRating->getStandardDeviation());
-        };
+        $varianceGetter = fn($currentRating) => BasicMath::square($currentRating->getStandardDeviation());
 
         $team1MeanSum = BasicMath::sum($team1Ratings, $meanGetter);
         $team1StdDevSquared = BasicMath::sum($team1Ratings, $varianceGetter);