+
+ // If there is an enemy rook or queen attacking the pawn from behind,
+ // add all X-ray attacks by the rook or queen.
+ if(bit_is_set(ei.attacked_by(them,ROOK)|ei.attacked_by(them,QUEEN),s)
+ && squares_behind(us, s) & pos.rooks_and_queens(them))
+ b3 = b2;
+