(;AB[gr]AB[gs]AB[ks]AB[fq]AB[er]AW[gq]AW[hq]AW[iq]AW[jq]AW[kq]AW[mq]AW[fp]AB[ep]AW[gp]AW[ns]AW[nr]C[Please show black why the invasion at A is a mistake. It should have been at B, at the most.]LB[ks:A]LB[js:B]AP[goproblems]
(;W[is];B[ir]
(;W[jr];B[hr];W[js]C[Not the best, as you ended in gote and lost quite some territory.])
(;W[hr];B[hs];W[jr]C[RIGHT])
(;W[js];B[jr]
(;W[hr];B[hs])
(;W[kr];B[hs]))
(;W[kr];B[js]
(;W[hr];B[hs])
(;W[hs];B[hr])
(;W[jr];B[hs])))
(;W[js];B[jr]
(;W[ir];B[is]
(;W[hs];B[hr])
(;W[hr];B[hs])
(;W[kr];B[js]
(;W[hs];B[hr])
(;W[ls];B[hs])))
(;W[kr];B[is])
(;W[is];B[ir]
(;W[hr];B[hs])
(;W[kr];B[hs]))
(;W[ls];B[is]))
(;W[ir];B[is])
(;W[jr];B[is];W[js]C[You could have done better, as you ended in gote and still had some territory reduction.])
(;W[hs];B[hr]
(;W[ir];B[is])
(;W[is];B[ir])
(;W[js];B[jr]
(;W[ir];B[is])
(;W[is];B[ir]))
(;W[jr];B[js]
(;W[is];B[ir])
(;W[ir];B[is])))
(;W[hr];B[hs]
(;W[is]C[This is probably the best.RIGHT])
(;W[js];B[jr]
(;W[ir];B[is])
(;W[is];B[ir]))
(;W[jr];B[js];W[is];B[ir]C[Ko, instead of killing black in your territory unconditionally.]))
(;W[kr];B[is]))