def gen_ret_lin_capacity_rule(mod, g, p):
    """
    **Expressions Name**: GenRetLin_Capacity_MW
    **Enforced Over**: GEN_RET_LIN_OPR_PRDS

    Existing capacity minus retirements.
    """
    return mod.gen_ret_lin_capacity_mw[g, p] - mod.GenRetLin_Retire_MW[g, p]