exchange_contrib_ksym Function

    HElement_t(dp) function exchange_contrib_ksym(nI, J, p, q, a, spin)
        ! sym-symbol version of above!
        ! BUT here: p and q are the symbols of the electrons and q is the
        ! symbol of 1 hole! so i have to call this function also for the
        ! exchanged version!
        integer, intent(in) :: nI(:), spin
        real(dp), intent(in) :: J
        type(symmetry), intent(in) :: p, q, a
#ifdef DEBUG_
        character(*), parameter :: this_routine = "exchange_contrib_ksym"
#endif
        type(symmetry) :: k1, k2

        ASSERT(spin == -1 .or. spin == 1)

        k1 = SymTable(p%s, q%s)
        ! the subtraction has something to do with the inputted spin!!
        ! todo
        ! spin is chosen from p momentum! so a is the p-k = a hole
        ! and we need the dipersion of p-k - q = a - q
        k2 = SymTable(a%s, SymConjTab(q%s))

        exchange_contrib_ksym = 2.0_dp * real(bhub, dp) * (cosh(J) - 1.0_dp) / real(omega, dp) &
                                * (get_one_body_diag(nI, -spin, k1, .true.) + get_one_body_diag(nI, -spin, k2))

    end function exchange_contrib_ksym