subset_integer_int64 Function

    pure function subset_integer_int64 (A, B) result(res)
        integer (int64), intent(in) :: A(:), B(:)
        logical :: res
        character(*), parameter :: this_routine = "subset_integer_int64"

        integer :: i, j

#ifdef DEBUG_
    block
        use util_mod, only: stop_all
        if (.not. (is_sorted(A))) then
            call stop_all (this_routine, "Assert fail: is_sorted(A)")
        end if
    end block
#endif
#ifdef DEBUG_
    block
        use util_mod, only: stop_all
        if (.not. (is_sorted(B))) then
            call stop_all (this_routine, "Assert fail: is_sorted(B)")
        end if
    end block
#endif

        if (size(A) == 0) then
            res = .true.
            return
        end if

        res = .false.

        if (size(A) > size(B)) return
        if (A(1) < B(1) .or. A(size(A)) > B(size(B))) return

        i = 1; j = 1
        do while (i <= size(A))
            if (j > size(B)) then
                return
            else if (i == size(A) .and. j == size(B) .and. A(i) /= B(j)) then
                return
            else if (A(i) < B(j)) then
                i = i + 1
            else if (A(i) > B(j)) then
                j = j + 1
            else if (A(i) == B(j)) then
                i = i + 1
                j = j + 1
            end if
        end do
        res = .true.
    end function subset_integer_int64