inline Bitboard line_bb(Square s1, Square s2) {
assert(is_ok(s1) && is_ok(s2));
+
return LineBB[s1][s2];
}
/// interpose itself to cover the check or capture the checking piece.
inline Bitboard between_bb(Square s1, Square s2) {
+
assert(is_ok(s1) && is_ok(s2));
+
return BetweenBB[s1][s2];
}