Type st2 = types.memberType(site, s2);
closure(site, supertypes);
for (Type t : supertypes.values()) {
for (Scope.Entry e = t.tsym.members().lookup(s1.name); e.scope != null; e = e.next()) {
Symbol s3 = e.sym;
if (s3 == s1 || s3 == s2 || s3.kind != MTH || (s3.flags() & (BRIDGE|SYNTHETIC)) != 0) continue;
Type st3 = types.memberType(site,s3);
if (types.overrideEquivalent(st3, st1) &&
types.overrideEquivalent(st3, st2) &&
types.returnTypeSubstitutable(st3, st1) &&
types.returnTypeSubstitutable(st3, st2)) {