fix(library/unifier): typo

fixes #588

src/library/unifier.cpp

@@ -1359,7 +1359,7 @@ struct unifier_fn {
         expr rhs_fn     = get_app_rev_args(rhs, rhs_args);
         declaration d   = *m_env.find(const_name(lhs_fn));
         levels lhs_lvls = const_levels(lhs_fn);
-        levels rhs_lvls = const_levels(lhs_fn);
+        levels rhs_lvls = const_levels(rhs_fn);
         if (length(lhs_lvls) != length(rhs_lvls) ||
             d.get_num_univ_params() != length(lhs_lvls)) {
             // the constraint is not well-formed, this can happen when users are abusing the API

tests/lean/run/588.lean

@@ -0,0 +1,20 @@
+import standard
+open function
+
+variables {a b r : Type}
+
+definition f a := Πr, (a -> r) -> r
+
+definition g (fn : a -> b) (sa : f a) : f b := sorry
+
+-- ok
+check λx, g id x = x
+
+check λ(x : f a), g id x = x
+
+universe variables l₁ l₂ l₃
+
+check λ (x : f.{_ l₂} a), g.{_ _ l₂ l₂} id x = x
+
+example (x : f a) : g id x = x :=
+sorry