C++
Listing 1.
A min() Function Using Concepts: The min() function is a constrained template with a single LessThanComparable requirement, whose concept specifies the less-than operator. 
concept LessThanComparable<typename T> {
  bool operator<(const T& x, const T& y);
}

template<typename T>
requires LessThanComparable<T>
const T& min(const T& x, const T& y) {
  return x < y? x : y;
}