std::unstoppable_token

template< class Token >
concept unstoppable_token =
    std::stoppable_token<Token> &&
    requires (const Token tok) {
        requires std::bool_constant<(!tok.stop_possible())>::value;
    };

The concept unstoppable_token<Token> specifies an additional requirement for a stoppable_token where the type does not allow stopping. That is, the expression tok.stop_possible() must be usable in constant expression and returns false.