diff --git a/crates/erg_compiler/context/unify.rs b/crates/erg_compiler/context/unify.rs
index 8a7c60915..fea7e0dcc 100644
--- a/crates/erg_compiler/context/unify.rs
+++ b/crates/erg_compiler/context/unify.rs
@@ -1298,6 +1298,7 @@ impl<'c, 'l, 'u, L: Locational> Unifier<'c, 'l, 'u, L> {
                 // self.sub_unify(&lsub, &union, loc, param_name)?;
                 maybe_sup.update_tyvar(union, intersec, self.undoable, false);
             }
+            // TODO: Preferentially compare same-structure types (e.g. K(?T) <: K(?U))
             (And(ltys), And(rtys)) => {
                 let mut ltys_ = ltys.clone();
                 let mut rtys_ = rtys.clone();
@@ -1322,6 +1323,7 @@ impl<'c, 'l, 'u, L: Locational> Unifier<'c, 'l, 'u, L> {
                     }
                 }
             }
+            // TODO: Preferentially compare same-structure types (e.g. K(?T) <: K(?U))
             // Nat or Str or NoneType <: NoneType or ?T or Int
             // => Str <: ?T
             // (Int or ?T) <: (?U or Int)