Non-type template parameters and requires

If you only have a boolean condition and nothing else, do this:

template<Bla b>
requires(b > 1)
void f() {}

Alternative longer syntax, if you need to check more things in the same requires-expression:

template<Bla b>
requires requires
{
    requires b > 1;
//  ^~~~~~~~
}
void f() {}

Since f needs to be constrained only by the value of the non-type template parameter, you can simply write a requires clause instead of an ad-hoc requires requires constraint:

template<Bla b>
requires (b>1) 
void f() {}

Here's a demo.

You only need a requires requires expression if you want to do more complicated checks on the template parameter. In that case, I recommend using a named concept over an ad-hoc constraint anyway. This makes the code more readable, and allows you to reuse the concept in other places.

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As for assert, it's a run-time construct, so it doesn't affect compilation in any way, assuming the expression inside the assert is syntactically valid. You need to use static_assert instead, if you want to check the template parameter at compile time:

static_assert(b>1);