is_in_ref Function

    logical function is_in_ref(orb, part_type)
        ! write a function if a certain orbital is in the reference
        ! determinant of replica part_type
        integer, intent(in) :: orb
        integer, intent(in), optional :: part_type

        integer :: temp_part_type
        integer(n_int) :: temp_ilut(0:niftot)

        if (present(part_type)) then
            temp_part_type = part_type
        else
            temp_part_type = 1
        end if

        ! there is an inefficient way to check projedet:

        temp_ilut = ilutref(:, part_type_to_run(temp_part_type))
        is_in_ref = (IsOcc(temp_ilut, orb))

    end function is_in_ref