On Sat, 25 Feb 2023 at 18:59, Jason McKesson via Std-Proposals
<std-proposals_at_[hidden]> wrote:
> C++0x concepts required definition checking; that was a core pillar of
> the feature. C++20 concepts did not. This means that the C++20 concept
> feature was able to look at concept strategies that would make
> definition checking functionally *impossible*. And... that's what we
> have now: a concept feature that is good and useful, but can *never*
> have definition checking.

Why not? You declare your template to be definition-checked, and that
then means it goes to the C++0x rules
which means it refuses to use other templates that aren't similarly
declared definition-checked.