bool
operator!=(
    ipv4_address const& a1,
    ipv4_address const& a2) noexcept;

bool
operator!=(
    ipv6_address const& a1,
    ipv6_address const& a2) noexcept;

bool
operator!=(
    authority_view const& a0,
    authority_view const& a1) noexcept;

template<
    class S0,
    class S1>
constexpr
bool
operator!=(
    S0 const& s0,
    S1 const& s1) noexcept;

bool
operator!=(
    iterator const& it0,
    iterator const& it1) noexcept;

bool
operator!=(
    url_view_base const& u0,
    url_view_base const& u1) noexcept;