operator!=

template<class BidIt, class T, class Ref, class Ptr, class Dist>
    bool operator!=(
        const reverse_bidirectional_iterator<BidIt, T, Ref,
            Ptr, Dist>& lhs,
        const reverse_bidirectional_iterator<BidIt, T, Ref,
            Ptr, Dist>& rhs);
template<class RanIt, class T, class Ref, class Ptr, class Dist>
    bool operator!=(
        const reverse_iterator<BidIt, T, Ref, Ptr, Dist>& lhs,
        const reverse_iterator<BidIt, T, Ref, Ptr, Dist>& rhs);
template<class T, class Dist>
    bool operator!=(
        const istream_iterator<T, Dist>& lhs,
        const istream_iterator<T, Dist>& rhs);
template<class E, class T>
    bool operator!=(
        const istreambuf_iterator<E, T>& lhs,
        const istreambuf_iterator<E, T>& rhs);

The template operator returns !(lhs == rhs).