I've just prefixed the declarator-id, but that exhibits an issue: While the concept names are all in namespace std (good), the return types such as safe_iterator_t or blah_result are not; they are in namespace std::ranges. There are three approaches:

• transform to trailing return types
• qualify the return type with "ranges::", too
• ignore the issue and assume (contrary to compiler behavior) that names in the return type are resolved by starting lookup in the declarator-id's namespace.

Editorial meeting:

• If there is a possibility of confusion, qualify declarator-id and return type etc. No "namespace { }".
• Otherwise, no change.

Rebased and return types qualified.