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Theorem dedlemb 994
 Description: Lemma for weak deduction theorem. See also ifpfal 1018. (Contributed by NM, 15-May-1999.) (Proof shortened by Andrew Salmon, 7-May-2011.)
Assertion
Ref Expression
dedlemb 𝜑 → (𝜒 ↔ ((𝜓𝜑) ∨ (𝜒 ∧ ¬ 𝜑))))

Proof of Theorem dedlemb
StepHypRef Expression
1 olc 398 . . 3 ((𝜒 ∧ ¬ 𝜑) → ((𝜓𝜑) ∨ (𝜒 ∧ ¬ 𝜑)))
21expcom 450 . 2 𝜑 → (𝜒 → ((𝜓𝜑) ∨ (𝜒 ∧ ¬ 𝜑))))
3 pm2.21 119 . . . 4 𝜑 → (𝜑𝜒))
43adantld 482 . . 3 𝜑 → ((𝜓𝜑) → 𝜒))
5 simpl 472 . . . 4 ((𝜒 ∧ ¬ 𝜑) → 𝜒)
65a1i 11 . . 3 𝜑 → ((𝜒 ∧ ¬ 𝜑) → 𝜒))
74, 6jaod 394 . 2 𝜑 → (((𝜓𝜑) ∨ (𝜒 ∧ ¬ 𝜑)) → 𝜒))
82, 7impbid 201 1 𝜑 → (𝜒 ↔ ((𝜓𝜑) ∨ (𝜒 ∧ ¬ 𝜑))))
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 195   ∨ wo 382   ∧ wa 383 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8 This theorem depends on definitions:  df-bi 196  df-or 384  df-an 385 This theorem is referenced by:  pm4.42  995  elimhOLD  1027  iffalse  4045
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