Method operator!=

gil/gil.impl.hpp:271–271

struct None {
  constexpr auto operator==(None) const noexcept { return Value<true>{}; }
  constexpr auto operator!=(None) const noexcept { return Value<false>{}; }
  template <typename T> friend constexpr auto operator==(None, T) noexcept {
    return Value<false>{};
  }