33 Concurrency support library [thread]

33.2 Requirements [thread.req]

33.2.1 Template parameter names [thread.req.paramname]

Throughout this Clause, the names of template parameters are used to express type requirements.
Predicate is a function object type ([function.objects]).
Let pred denote an lvalue of type Predicate.
Then the expression pred() shall be well-formed and the type decltype(pred()) shall model boolean-testable ([concept.booleantestable]).
The return value of pred(), converted to bool, yields true if the corresponding test condition is satisfied, and false otherwise.
If a template parameter is named Clock, the corresponding template argument shall be a type C that meets the Cpp17Clock requirements ([time.clock.req]); the program is ill-formed if is_clock_v<C> is false.