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Theorem axc5c711 34719
 Description: Proof of a single axiom that can replace ax-c5 34684, ax-c7 34686, and ax-11 2189 in a subsystem that includes these axioms plus ax-c4 34685 and ax-gen 1869 (and propositional calculus). See axc5c711toc5 34720, axc5c711toc7 34721, and axc5c711to11 34722 for the rederivation of those axioms. This theorem extends the idea in Scott Fenton's axc5c7 34712. (Contributed by NM, 18-Nov-2006.) (Proof modification is discouraged.) (New usage is discouraged.)
Assertion
Ref Expression
axc5c711 ((∀𝑥𝑦 ¬ ∀𝑥𝑦𝜑 → ∀𝑥𝜑) → 𝜑)

Proof of Theorem axc5c711
StepHypRef Expression
1 ax-c5 34684 . . 3 (∀𝑦𝜑𝜑)
2 ax10fromc7 34696 . . . 4 (¬ ∀𝑦𝜑 → ∀𝑦 ¬ ∀𝑦𝜑)
3 ax-c7 34686 . . . . . 6 (¬ ∀𝑥 ¬ ∀𝑥𝑦𝜑 → ∀𝑦𝜑)
43con1i 146 . . . . 5 (¬ ∀𝑦𝜑 → ∀𝑥 ¬ ∀𝑥𝑦𝜑)
54alimi 1886 . . . 4 (∀𝑦 ¬ ∀𝑦𝜑 → ∀𝑦𝑥 ¬ ∀𝑥𝑦𝜑)
6 ax-11 2189 . . . 4 (∀𝑦𝑥 ¬ ∀𝑥𝑦𝜑 → ∀𝑥𝑦 ¬ ∀𝑥𝑦𝜑)
72, 5, 63syl 18 . . 3 (¬ ∀𝑦𝜑 → ∀𝑥𝑦 ¬ ∀𝑥𝑦𝜑)
81, 7nsyl4 157 . 2 (¬ ∀𝑥𝑦 ¬ ∀𝑥𝑦𝜑𝜑)
9 ax-c5 34684 . 2 (∀𝑥𝜑𝜑)
108, 9ja 174 1 ((∀𝑥𝑦 ¬ ∀𝑥𝑦𝜑 → ∀𝑥𝜑) → 𝜑)
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3  ∀wal 1628 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1869  ax-4 1884  ax-11 2189  ax-c5 34684  ax-c4 34685  ax-c7 34686 This theorem is referenced by:  axc5c711toc5  34720  axc5c711toc7  34721  axc5c711to11  34722
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