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% nacteni: /* ['7.2_15.pl']. */ alphabeta(Pos, Alpha, Beta, GoodPos, Val) :- moves( Pos, PosList), !, boundedbest( PosList, Alpha, Beta, GoodPos, Val); staticval(Pos, Val ). % Static value of Pos boundedbest([Pos | PosList], Alpha, Beta, GoodPos, GoodVal) :- alphabeta(Pos, Alpha, Beta,_ , Val ), goodenough(PosList, Alpha, Beta, Pos, Val, GoodPos, GoodVal). goodenough([],_,_, Pos, Val, Pos, Val) :- ! . % No other candidate goodenough(_, Alpha, Beta, Pos, Val, Pos, Val) :- min_to_move(Pos), Val > Beta, ! % Maximizer attained upper bound ; max_to_move(Pos), Val < Alpha, !. % Minimizer attained lower bound goodenough(PosList, Alpha, Beta, Pos, Val, GoodPos, GoodVal) :- newbounds(Alpha, Beta, Pos, Val, NewAlpha, NewBeta), % Refine bounds boundedbest(PosList, NewAlpha, NewBeta, Pos1, Val1), betterof(Pos, Val, Pos1, Val1, GoodPos, GoodVal). newbounds( Alpha, Beta, Pos, Val, Val, Beta) :- min_to_move( Pos), Val > Alpha, !. % Maximizer increased lower bound newbounds( Alpha, Beta, Pos, Val, Alpha, Val) :- max_to_move( Pos), Val < Beta, !. % Minimizer decreased upper bound newbounds( Alpha, Beta, _, _, Alpha, Beta). % Otherwise bounds unchanged betterof(Pos, Val, _Pos1, Val1, Pos, Val) :- min_to_move( Pos), Val > Val1, ! ; max_to_move( Pos), Val < Val1, !. % Pos better than Pos1 betterof(_,_, Pos1, Val1, Pos1, Val1). % Otherwise Pos1 better
true