theorem discretion_zero_cost_of_appearing {c phi_prev sigma_old sigma_new delta : ℝ}
(hs1 : sigma_old ≠ 0) (hs2 : sigma_new ≠ 0) :
discretionaryGain c phi_prev sigma_old sigma_new delta = 0 :=
discretionary_gain_zero hs1 hs2Time Inconsistency Resolution via Upstream Reform (Gap 11)