Theorem wl-19.8eqv 34928

Description: Under the assumption ¬ 𝑥 = 𝑦 a specialized version of 19.8a 2178 is provable from Tarski's FOL and ax13v 2380 only. Note that this reverts the implication in ax13lem2 2383, so in fact (¬ 𝑥 = 𝑦 → (∃𝑥𝑧 = 𝑦 ↔ 𝑧 = 𝑦)) holds. (Contributed by Wolf Lammen, 17-Apr-2021.)

Assertion

Ref	Expression
wl-19.8eqv	⊢ (¬ 𝑥 = 𝑦 → (𝑧 = 𝑦 → ∃𝑥 𝑧 = 𝑦))

Distinct variable group:   𝑥,𝑧

Proof of Theorem wl-19.8eqv

Step	Hyp	Ref	Expression
1		ax13lem1 2381	. 2 ⊢ (¬ 𝑥 = 𝑦 → (𝑧 = 𝑦 → ∀𝑥 𝑧 = 𝑦))
2		19.2 1981	. 2 ⊢ (∀𝑥 𝑧 = 𝑦 → ∃𝑥 𝑧 = 𝑦)
3	1, 2	syl6 35	1 ⊢ (¬ 𝑥 = 𝑦 → (𝑧 = 𝑦 → ∃𝑥 𝑧 = 𝑦))

Syntax hints:  ¬ wn 3   → wi 4  ∀wal 1536  ∃wex 1781

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 1911  ax-6 1970  ax-7 2015  ax-13 2379

This theorem depends on definitions:  df-bi 210  df-an 400  df-ex 1782

This theorem is referenced by: (None)