ids' = map (\id -> id `setIdType` substTy subst (idType id)) ids
subst_dom= varEnvKeys$ getTvSubstEnv subst
subst_ran= varEnvElts$ getTvSubstEnv subst
ids' = map (\id -> id `setIdType` substTy subst (idType id)) ids
subst_dom= varEnvKeys$ getTvSubstEnv subst
subst_ran= varEnvElts$ getTvSubstEnv subst