-> CanonicalCts -- Unsolved
-> [[(CanonicalCt,TcTyVar)]]
findDefaultableGroups (ctxt, default_tys, (ovl_strings, extended_defaults))
-> CanonicalCts -- Unsolved
-> [[(CanonicalCt,TcTyVar)]]
findDefaultableGroups (ctxt, default_tys, (ovl_strings, extended_defaults))