Returns true if all the elements in the range position1, number1 are equivalent to some element in position0, number0. The comparison uses comparator to test this; The value of an element, a, is equivalent to another one, b, when (not comparator.evaluate(a, b) and not comparator(b, a)). For the function to yield the expected result, the elements in the ranges shall be already ordered according to the same strict weak ordering criterion ( comparator). C++ template example: bool includes ( InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2 ) { while (first1!=last1) { if (*first2<*first1) break; else if (*first1<*first2) ++first1; else { ++first1; ++first2; } if (first2==last2) return true; } return false; } Returns true if every element in the range position1, number1 is contained in the range position0, number0, false otherwise.