A black play at 'B' will convert this moyo into a large territory. ------------------- White invasion urgent!
NOTE: Several white moves that may lead to life are blocked. I'd appreciate anyone showing why any of these are equal, or inferior, to the solution.
(;AB[pj][jp][mp][pp]LB[qq:A][qp:B][ro:C][ql:D]
C[White can invade at any of the labelled points, but only 'A' is considered here. ---- Please play at 'A' to start. FORCE]
;W[qq];B[qp]
(;W[rp];B[ro];W[rr];B[sp];W[sq]C[You got a ko, but unconditional life in sente is possible.])
(;W[rq]C[NOTTHIS])
(;W[pq];B[nq]
(;W[nr]C[NOTTHIS])
(;W[op]C[NOTTHIS])
(;W[oq]C[NOTTHIS])
(;W[or]C[NOTTHIS])
(;W[rp];B[ro]
(;W[nr]C[NOTTHIS])
(;W[op]C[NOTTHIS])
(;W[oq]C[NOTTHIS])
(;W[or]C[NOTTHIS])
(;W[rr];B[sp];W[sq]C[The ko is not required, as white can live in sente unconditionally.])
(;W[rq];B[qn]
C[RIGHT White has made ~5 points, ruined black's corner, caused overconcentration of his forces, and kept sente. The
invasion is worth ~25 points.]))
(;W[rq];B[rp]
(;W[oq];B[op];W[nr];B[mr];W[or]C[You live in gote. The reduction in black's territory
is similar to the solution, but loss of sente makes this inferior.])
(;W[nr];B[mr];W[oq];B[op];W[or]C[You live in gote. The reduction in black's territory
is similar to the solution, but loss of sente makes this inferior.])))
(;W[pr];B[pq];W[rr];B[or];W[rp];B[ro]LB[qs:A][sq:B]C[You can leave a ko behind, or live playing 'A' or 'B'. The reduction
in black's territory is ~6 points smaller than the solution.]))