template <class T1, class T2>
bool operator==(const polymorphic_allocator<T1>& a,
const polymorphic_allocator<T2>& b) noexcept;
template <class T1, class T2>
bool operator!=(const polymorphic_allocator<T1>& a,
const polymorphic_allocator<T2>& b) noexcept;