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#include <iostream>

// CRTP base that provides operator!= and operator> from operator== and operator<
template<typename Derived>
class Comparable {
public:
    bool operator!=(const Derived& rhs) const {
        return !(static_cast<const Derived&>(*this) == rhs);
    }
    bool operator>(const Derived& rhs) const {
        return rhs < static_cast<const Derived&>(*this);
    }
    bool operator<=(const Derived& rhs) const {
        return !(static_cast<const Derived&>(*this) > rhs);
    }
    bool operator>=(const Derived& rhs) const {
        return !(static_cast<const Derived&>(*this) < rhs);
    }
};

class Temperature : public Comparable<Temperature> {
public:
    explicit Temperature(double celsius) : celsius_(celsius) {}

bool operator==(const Temperature& rhs) const {
        return celsius_ == rhs.celsius_;
    }
    bool operator<(const Temperature& rhs) const {
        return celsius_ < rhs.celsius_;
    }

double value() const { return celsius_; }

private:
    double celsius_;
};

int main() {
    Temperature t1(20.0), t2(35.0);

std::cout << std::boolalpha;
    std::cout << "t1 < t2:  " << (t1 < t2)  << "
";  // true
    std::cout << "t1 > t2:  " << (t1 > t2)  << "
";  // false
    std::cout << "t1 != t2: " << (t1 != t2) << "
";  // true
    std::cout << "t1 <= t2: " << (t1 <= t2) << "
";  // true

return 0;
}