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Theorem dedlem0a 991
 Description: Lemma for an alternate version of weak deduction theorem. (Contributed by NM, 2-Apr-1994.) (Proof shortened by Andrew Salmon, 7-May-2011.) (Proof shortened by Wolf Lammen, 4-Dec-2012.)
Assertion
Ref Expression
dedlem0a (𝜑 → (𝜓 ↔ ((𝜒𝜑) → (𝜓𝜑))))

Proof of Theorem dedlem0a
StepHypRef Expression
1 iba 523 . 2 (𝜑 → (𝜓 ↔ (𝜓𝜑)))
2 ax-1 6 . . 3 (𝜑 → (𝜒𝜑))
3 biimt 349 . . 3 ((𝜒𝜑) → ((𝜓𝜑) ↔ ((𝜒𝜑) → (𝜓𝜑))))
42, 3syl 17 . 2 (𝜑 → ((𝜓𝜑) ↔ ((𝜒𝜑) → (𝜓𝜑))))
51, 4bitrd 267 1 (𝜑 → (𝜓 ↔ ((𝜒𝜑) → (𝜓𝜑))))
 Colors of variables: wff setvar class Syntax hints:   → wi 4   ↔ wb 195   ∧ 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-an 385 This theorem is referenced by:  iftrue  4042
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