(;
AB[mn][qn][oo][po][ro][pq][rr]
AW[np][nq][pp][qp][lq][rq][sr]
C[Black plays.]
(;
B[op]
C[Splitting White's stones is a good option for Black.];
W[oq];B[pr]
C[The key idea for giving Black enough liberties.];
W[or];B[qr];W[rp];B[rs]
C[Black makes a 2nd empty triangle to set up a defensive shape.];
W[ps];B[sp];W[os];B[so];W[sq]
C[Black saves the corner stones with a sente seki.]
)
    (;
    B[qq]
    C[Black has another option here.];
    W[rp];B[op];W[oq];B[rs]
    (;
    W[pr];B[qr];W[os];B[sp];W[qs]
    C[Black can start a relatively big ko and even takes 1st.  With enough ko threats, Black can capture the 5 stones for territory, instead of the seki in the main line.]
    )
        (;
        W[ps]
        C[Mistake.];
        B[qr]
        C[Black makes 2 empty triangles with one move, but ...];
        W[pr];B[or];W[nr];B[sq];W[os];B[qo];W[sp];B[so]
        C[... Black wins the semeai.]
        )
    )
)

