void GoRegion::Find2FreeLibs(const GoChain* c1, const GoChain* c2, SgPoint* lib1, SgPoint* lib2) const { SgPointSet libs = Points() & c1->FreeLiberties() & c2->FreeLiberties(); if (CHECK) SG_ASSERT(libs.MinSetSize(2)); SgSetIterator it(libs); *lib1 = *it; ++it; *lib2 = *it; }