x = y → y = y T → x = y → y = y ∀ (x_1 : T), x = x_1 → x_1 = y ∀ (x_1 : T), x_1 = x → x = x T → T → x = y → y = y T → T → x = y → P y (∀ (x : T), P x ↔ Q x) → Q x Prop → (∀ (x : T), P x ↔ Q x) → Prop → Q x ∀ (x_1 : Prop), (∀ (x : T), P x ↔ Q x) → x_1 ∨ Q x (∀ (x : T), P x ↔ Q x) → Q x ∀ (x : T), T → (∀ (x : T), P x ↔ Q x) → Q x ∀ (x x_1 : T), x = x_1 → P x_1 ∀ (x x_1 x_2 : T), x = x_1 → x_1 = x_2 → P x_2 ∀ (x x_1 : T), x = x_1 → (∀ (w : T), P w ↔ Q w) → Q x_1