subst_dom= varEnvKeys$ getTvSubstEnv subst
subst_ran= varEnvElts$ getTvSubstEnv subst
new_tvs = [ tv | t <- subst_ran, let Just tv = getTyVar_maybe t]
ic_tyvars'= (`delVarSetListByKey` subst_dom)
. (`extendVarSetList` new_tvs)
$ ic_tyvars ictxt
subst_dom= varEnvKeys$ getTvSubstEnv subst
subst_ran= varEnvElts$ getTvSubstEnv subst
new_tvs = [ tv | t <- subst_ran, let Just tv = getTyVar_maybe t]
ic_tyvars'= (`delVarSetListByKey` subst_dom)
. (`extendVarSetList` new_tvs)
$ ic_tyvars ictxt