Theorem hba1-o 34686

Description: The setvar 𝑥 is not free in ∀𝑥𝜑. Example in Appendix in [Megill] p. 450 (p. 19 of the preprint). Also Lemma 22 of [Monk2] p. 114. (Contributed by NM, 24-Jan-1993.) (New usage is discouraged.)

Assertion

Ref	Expression
hba1-o	⊢ (∀𝑥𝜑 → ∀𝑥∀𝑥𝜑)

Proof of Theorem hba1-o

Step	Hyp	Ref	Expression
1		ax-c5 34672	. . 3 ⊢ (∀𝑥 ¬ ∀𝑥𝜑 → ¬ ∀𝑥𝜑)
2	1	con2i 134	. 2 ⊢ (∀𝑥𝜑 → ¬ ∀𝑥 ¬ ∀𝑥𝜑)
3		ax10fromc7 34684	. 2 ⊢ (¬ ∀𝑥 ¬ ∀𝑥𝜑 → ∀𝑥 ¬ ∀𝑥 ¬ ∀𝑥𝜑)
4		ax10fromc7 34684	. . . 4 ⊢ (¬ ∀𝑥𝜑 → ∀𝑥 ¬ ∀𝑥𝜑)
5	4	con1i 144	. . 3 ⊢ (¬ ∀𝑥 ¬ ∀𝑥𝜑 → ∀𝑥𝜑)
6	5	alimi 1888	. 2 ⊢ (∀𝑥 ¬ ∀𝑥 ¬ ∀𝑥𝜑 → ∀𝑥∀𝑥𝜑)
7	2, 3, 6	3syl 18	1 ⊢ (∀𝑥𝜑 → ∀𝑥∀𝑥𝜑)

Syntax hints:  ¬ wn 3   → wi 4  ∀wal 1630

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1871  ax-4 1886  ax-c5 34672  ax-c4 34673  ax-c7 34674

This theorem is referenced by:  axc4i-o  34687  nfa1-o  34704  axc711toc7  34705  axc5c711toc7  34709  dvelimf-o  34718  ax12indalem  34734  ax12inda2ALT  34735  ax12inda  34737