co2 = rwi_co eq2
-- rule would match with eq1 and eq2 swapped => put eq2 into todo list
-applySubstVarFam eq1@(RewriteFam {rwi_fam = fam1, rwi_args = args1})
+applySubstVarFam (RewriteFam {rwi_args = args1})
eq2@(RewriteVar {rwi_var = tv2})
| tv2 `elemVarSet` tyVarsOfTypes args1
= return $ Just eq2