Single killer move

src/Lynx/Search/Helpers.cs

@@ -124,16 +124,6 @@ internal int ScoreMove(Move move, int depth, bool useKillerAndPositionMoves, Mov
                 return EvaluationConstants.FirstKillerMoveValue;
             }
 
-            if (_killerMoves[1, depth] == move)
-            {
-                return EvaluationConstants.SecondKillerMoveValue;
-            }
-
-            if (_killerMoves[2, depth] == move)
-            {
-                return EvaluationConstants.ThirdKillerMoveValue;
-            }
-
             // History move or 0 if not found
             return EvaluationConstants.BaseMoveScore + _historyMoves[move.Piece(), move.TargetSquare()];
         }

src/Lynx/Search/IDDFS.cs

@@ -10,7 +10,7 @@ public sealed partial class Engine
 {
     private readonly Stopwatch _stopWatch = new();
     private readonly Move[] _pVTable = new Move[Configuration.EngineSettings.MaxDepth * (Configuration.EngineSettings.MaxDepth + 1) / 2];
-    private readonly int[,] _killerMoves = new int[3, Configuration.EngineSettings.MaxDepth];
+    private readonly int[,] _killerMoves = new int[1, Configuration.EngineSettings.MaxDepth];
     private readonly int[,] _historyMoves = new int[12, 64];
     private readonly int[] _maxDepthReached = new int[Constants.AbsoluteMaxDepth];
     private TranspositionTable _tt = Array.Empty<TranspositionTableElement>();
@@ -21,7 +21,7 @@ public sealed partial class Engine
     private bool _isScoringPV;
 
     private SearchResult? _previousSearchResult;
-    private readonly int[,] _previousKillerMoves = new int[3, Configuration.EngineSettings.MaxDepth];
+    private readonly int[,] _previousKillerMoves = new int[1, Configuration.EngineSettings.MaxDepth];
 
     private readonly Move _defaultMove = default;
 
@@ -264,8 +264,6 @@ private int CheckPonderHit(ref SearchResult? lastSearchResult, int depth)
             for (int d = 0; d < Configuration.EngineSettings.MaxDepth - 2; ++d)
             {
                 _killerMoves[0, d] = _previousKillerMoves[0, d + 2];
-                _killerMoves[1, d] = _previousKillerMoves[1, d + 2];
-                _killerMoves[2, d] = _previousKillerMoves[2, d + 2];
             }
 
             // Re-search from depth 1

src/Lynx/Search/NegaMax.cs

@@ -314,8 +314,6 @@ private int NegaMax(int depth, int ply, int alpha, int beta, bool parentWasNullM
                 // 🔍 Killer moves
                 if (!move.IsCapture() && move.PromotedPiece() == default && move != _killerMoves[0, ply])
                 {
-                    _killerMoves[2, ply] = _killerMoves[1, ply];
-                    _killerMoves[1, ply] = _killerMoves[0, ply];
                     _killerMoves[0, ply] = move;
                 }