[FEN "r3r1k1/pppbqpp1/5n1p/3p4/P1nP3B/2PBP2P/2Q1NPP1/R4RK1 b -"]

15... b5 16. Qa2


w b wb bw | w b wb bw

b     an
    


15...b5      an
    


16. Qa2      an