[FEN "r3r1k1/pppb1pp1/3q3p/8/P1nPpN2/2P1P1BP/2Q2PP1/R4RK1 b -"]

18... a6 19. Rfd1


w b wb bw | w b wb bw

b     an
    


18...a6      an
    


19. Rfd1      an