Theorem dedlema 969

Description: Lemma for iftrue 3537. (Contributed by NM, 26-Jun-2002.) (Proof shortened by Andrew Salmon, 7-May-2011.)

Assertion

Ref	Expression
dedlema	⊢ (𝜑 → (𝜓 ↔ ((𝜓 ∧ 𝜑) ∨ (𝜒 ∧ ¬ 𝜑))))

Proof of Theorem dedlema

Step	Hyp	Ref	Expression
1		orc 712	. . 3 ⊢ ((𝜓 ∧ 𝜑) → ((𝜓 ∧ 𝜑) ∨ (𝜒 ∧ ¬ 𝜑)))
2	1	expcom 116	. 2 ⊢ (𝜑 → (𝜓 → ((𝜓 ∧ 𝜑) ∨ (𝜒 ∧ ¬ 𝜑))))
3		simpl 109	. . . 4 ⊢ ((𝜓 ∧ 𝜑) → 𝜓)
4	3	a1i 9	. . 3 ⊢ (𝜑 → ((𝜓 ∧ 𝜑) → 𝜓))
5		pm2.24 621	. . . 4 ⊢ (𝜑 → (¬ 𝜑 → 𝜓))
6	5	adantld 278	. . 3 ⊢ (𝜑 → ((𝜒 ∧ ¬ 𝜑) → 𝜓))
7	4, 6	jaod 717	. 2 ⊢ (𝜑 → (((𝜓 ∧ 𝜑) ∨ (𝜒 ∧ ¬ 𝜑)) → 𝜓))
8	2, 7	impbid 129	1 ⊢ (𝜑 → (𝜓 ↔ ((𝜓 ∧ 𝜑) ∨ (𝜒 ∧ ¬ 𝜑))))

Syntax hints:  ¬ wn 3   → wi 4   ∧ wa 104   ↔ wb 105   ∨ wo 708

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in2 615  ax-io 709

This theorem depends on definitions:  df-bi 117

This theorem is referenced by:  iftrue  3537