question: public final ArrayList < Move > removeNonOptimal ( Position pos , ArrayList < Move > moveList ) { ArrayList < Move > optimalMoves = new ArrayList < Move > ( ) ; ArrayList < Move > unknownMoves = new ArrayList < Move > ( ) ; final int MATE0 = 100000 ; int bestScore = - 1000000 ; UndoInfo ui = new UndoInfo ( ) ; for ( Move m : moveList ) { pos . makeMove ( m , ui ) ; int pliesToDraw = Math . max ( 100 - pos . halfMoveClock , 1 ) ; GtbProbeResult res = gtbProbe ( pos ) ; pos . unMakeMove ( m , ui ) ; if ( res . result == GtbProbeResult . UNKNOWN ) { unknownMoves . add ( m ) ; } else { int wScore ; if ( res . result == GtbProbeResult . WMATE ) { if ( res . pliesToMate <= pliesToDraw ) wScore = MATE0 - res . pliesToMate ; else wScore = 1 ; } else if ( res . result == GtbProbeResult . BMATE ) { if ( res . pliesToMate <= pliesToDraw ) wScore = - ( MATE0 - res . pliesToMate ) ; else wScore = - 1 ; } else { wScore = 0 ; } int score = pos . whiteMove ? wScore : - wScore ; if ( score > bestScore ) { optimalMoves . clear ( ) ; optimalMoves . add ( m ) ; bestScore = score ; } else if ( score == bestScore ) { optimalMoves . add ( m ) ; } else { } } } for ( Move m : unknownMoves ) optimalMoves . add ( m ) ; return ( optimalMoves . size ( ) < moveList . size ( ) ) ? optimalMoves : null ; }
target:  Return a list of all moves in moveList that are not known to be non-optimal. Returns null if no legal move could be excluded. 