ndependent :: PrjDict dom -> Env dom -> AST dom a -> Bool
independent pd env (Sym (prjVariable pd -> Just v)) = not (v `member` dependencies env)

independent :: PrjDict dom -> Env dom -> AST dom a -> Bool
independent pd env (Sym (prjVariable pd -> Just v)) = not (v `member` dependencies env)
independent pd env (Sym (prjVariable pd -> Just v)) = not (v `member` dependencies env)