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Theorem ax12a2-o 36126
 Description: Derive ax-c15 36065 from a hypothesis in the form of ax-12 2178, without using ax-12 2178 or ax-c15 36065. The hypothesis is weaker than ax-12 2178, with 𝑧 both distinct from 𝑥 and not occurring in 𝜑. Thus, the hypothesis provides an alternate axiom that can be used in place of ax-12 2178, if we also have ax-c11 36063, which this proof uses. As theorem ax12 2446 shows, the distinct variable conditions are optional. An open problem is whether we can derive this with ax-c11n 36064 instead of ax-c11 36063. (Contributed by NM, 2-Feb-2007.) (Proof modification is discouraged.) (New usage is discouraged.)
Hypothesis
Ref Expression
ax12a2-o.1 (𝑥 = 𝑧 → (∀𝑧𝜑 → ∀𝑥(𝑥 = 𝑧𝜑)))
Assertion
Ref Expression
ax12a2-o (¬ ∀𝑥 𝑥 = 𝑦 → (𝑥 = 𝑦 → (𝜑 → ∀𝑥(𝑥 = 𝑦𝜑))))
Distinct variable groups:   𝑥,𝑧   𝑦,𝑧   𝜑,𝑧
Allowed substitution hints:   𝜑(𝑥,𝑦)

Proof of Theorem ax12a2-o
StepHypRef Expression
1 ax-5 1912 . . 3 (𝜑 → ∀𝑧𝜑)
2 ax12a2-o.1 . . 3 (𝑥 = 𝑧 → (∀𝑧𝜑 → ∀𝑥(𝑥 = 𝑧𝜑)))
31, 2syl5 34 . 2 (𝑥 = 𝑧 → (𝜑 → ∀𝑥(𝑥 = 𝑧𝜑)))
43ax12v2-o 36125 1 (¬ ∀𝑥 𝑥 = 𝑦 → (𝑥 = 𝑦 → (𝜑 → ∀𝑥(𝑥 = 𝑦𝜑))))
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3   → wi 4  ∀wal 1536 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1797  ax-4 1811  ax-5 1912  ax-6 1971  ax-7 2016  ax-10 2146  ax-11 2162  ax-12 2178  ax-13 2391  ax-c5 36059  ax-c4 36060  ax-c7 36061  ax-c10 36062  ax-c11 36063  ax-c9 36066 This theorem depends on definitions:  df-bi 210  df-an 400  df-or 845  df-tru 1541  df-ex 1782  df-nf 1786 This theorem is referenced by: (None)
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