Requirements: Need a story for optional and repeated syntax pieces

https://code.world/#PnQkjrztp45GAom-7ardWUA fails to check, despite having two declarations that appear, at first glance, to match the template. At first, I thought this was a failure to consider non-toplevel declarations. But it's quite the opposite! The non-toplevel declaration of `b` matches. It's the declaration of `a` that fails to match! The reason: the template has no where clause, but the definition of `a` does have a where clause. Therefore, it's not a match.

This is surprising to me, but I'm not sure how to specify exactly the behavior that I do want.