Theorem bj-ax89 34515

Description: A theorem which could be used as sole axiom for the non-logical predicate instead of ax-8 2116 and ax-9 2124. Indeed, it is implied over propositional calculus by the conjunction of ax-8 2116 and ax-9 2124, as proved here. In the other direction, one can prove ax-8 2116 (respectively ax-9 2124) from bj-ax89 34515 by using mpan2 691 (respectively mpan 690) and equid 2024. TODO: move to main part. (Contributed by BJ, 3-Oct-2019.)

Assertion

Ref	Expression
bj-ax89	⊢ ((𝑥 = 𝑦 ∧ 𝑧 = 𝑡) → (𝑥 ∈ 𝑧 → 𝑦 ∈ 𝑡))

Proof of Theorem bj-ax89

Step	Hyp	Ref	Expression
1		ax8 2120	. 2 ⊢ (𝑥 = 𝑦 → (𝑥 ∈ 𝑧 → 𝑦 ∈ 𝑧))
2		ax9 2128	. 2 ⊢ (𝑧 = 𝑡 → (𝑦 ∈ 𝑧 → 𝑦 ∈ 𝑡))
3	1, 2	sylan9 511	1 ⊢ ((𝑥 = 𝑦 ∧ 𝑧 = 𝑡) → (𝑥 ∈ 𝑧 → 𝑦 ∈ 𝑡))

Syntax hints:   → wi 4   ∧ wa 399

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1802  ax-4 1816  ax-5 1917  ax-6 1975  ax-7 2020  ax-8 2116  ax-9 2124

This theorem depends on definitions:  df-bi 210  df-an 400  df-ex 1787

This theorem is referenced by: (None)