operator[]('B') = WB; operator[]('b') = BB;
operator[]('N') = WN; operator[]('n') = BN;
operator[]('P') = WP; operator[]('p') = BP;
operator[]('B') = WB; operator[]('b') = BB;
operator[]('N') = WN; operator[]('n') = BN;
operator[]('P') = WP; operator[]('p') = BP;