https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125605
--- Comment #1 from songb432 at gmail dot com ---
Oops, the copy from Compiler Explorer is incorrect. Here's the correct one:
```
namespace Example1 {
template<typename T>
concept A = T::value || true;
template<typename U>
concept B = A<U*>; // OK: normalized to the disjunction of
// - T::value (with mapping T -> U*) and
// - true (with an empty mapping).
// No invalid type in mapping even though
// T::value is ill-formed for all pointer types
template<typename V>
concept C = B<V&>; // Normalizes to the disjunction of
// - T::value (with mapping T-> V&*) and
// - true (with an empty mapping).
// Invalid type V&* formed in mapping => ill-formed NDR
static_assert(B<int>); // Shouldn't pass.
} // namespace Example1
namespace Example2 { // see also
https://eel.is/c++draft/temp.constr#op-example-2
template <class T> concept sad = true;
template <class T> concept sad_nested_type = sad<typename T::type>;
template <class T> int f(T) requires sad_nested_type<T> { return 0; }
//template <class T> int f(T) requires sad_nested_type<typename T::type>;
int i = f(42); // substitution failure contained within sad_nested_type
} // namespace Example2
namespace Example2_ { // see also
https://eel.is/c++draft/temp.constr#op-example-2
template <class T> concept sad = true;
template <class T> concept sad_nested_type = sad<typename T::type>;
template <class T> int f(T) requires sad_nested_type<T> { return 0; }
template <class T> int f(T) requires sad_nested_type<typename T::type>;
int i = f(42); // substitution failure contained within sad_nested_type
} // namespace Example2_
namespace Example3 { // see also
https://eel.is/c++draft/temp.constr#decl-example-2
template <class T> concept C = true;
template <class T> struct A {
template <class U> U f(U) requires C<typename T::type>; // #1
template <class U> U f(U) requires C<T>; // #2
};
using U = decltype(A<int>{}.f(2));
} // namespace Example3
int main() {}
```
