def slack_neg_rule(m, i, j, t):
    """
    If decision variable m.var_x[i, j, t] is set to FALSE, the negative slack varibale var_slack[i, j, t] is nonzero

    :param m: complete pyomo model
    :type m: pyomo model
    :param i: startnode index of set_edge
    :type i: int
    :param j: endnode index of set_edge
    :type j: int
    :param t: type index of set_linetypes
    :type t: int
    :returns:
        - **pyomo equality function**: pyomo rule
    :rtype: function

    """

    return (m.var_slack[i, j, t]) >= (-1) * (1 - m.var_x[i, j, t]) * 1000000