extendTvSubst :: TvSubst -> TyVar -> Type -> TvSubst
extendTvSubst (TvSubst in_scope tenv) tv ty = TvSubst in_scope (extendVarEnv tenv tv ty)
extendTvSubst :: TvSubst -> TyVar -> Type -> TvSubst
extendTvSubst (TvSubst in_scope tenv) tv ty = TvSubst in_scope (extendVarEnv tenv tv ty)
extendTvSubst (TvSubst in_scope tenv) tv ty = TvSubst in_scope (extendVarEnv tenv tv ty)