Theorem ax7v 2031

Description: Weakened version of ax-7 2030, with a disjoint variable condition on 𝑥, 𝑦. This should be the only proof referencing ax-7 2030, and it should be referenced only by its two weakened versions ax7v1 2032 and ax7v2 2033, from which ax-7 2030 is then rederived as ax7 2038, which shows that either ax7v 2031 or the conjunction of ax7v1 2032 and ax7v2 2033 is sufficient.

In ax7v 2031, it is still allowed to substitute the same variable for 𝑥 and 𝑧, or the same variable for 𝑦 and 𝑧. Therefore, ax7v 2031 "bundles" (a term coined by Raph Levien) its "principal instance" (𝑥 = 𝑦 → (𝑥 = 𝑧 → 𝑦 = 𝑧)) with 𝑥, 𝑦, 𝑧 distinct, and its "degenerate instances" (𝑥 = 𝑦 → (𝑥 = 𝑥 → 𝑦 = 𝑥)) and (𝑥 = 𝑦 → (𝑥 = 𝑦 → 𝑦 = 𝑦)) with 𝑥, 𝑦 distinct. These degenerate instances are for instance used in the proofs of equcomiv 2036 and equid 2034 respectively. (Contributed by BJ, 7-Dec-2020.) Use ax7 2038 instead. (New usage is discouraged.)

Assertion

Ref	Expression
ax7v	⊢ (𝑥 = 𝑦 → (𝑥 = 𝑧 → 𝑦 = 𝑧))

Distinct variable group:   𝑥,𝑦

Proof of Theorem ax7v

Step	Hyp	Ref	Expression
1		ax-7 2030	1 ⊢ (𝑥 = 𝑦 → (𝑥 = 𝑧 → 𝑦 = 𝑧))

Syntax hints:   → wi 4

This theorem was proved from axioms:  ax-7 2030

This theorem is referenced by:  ax7v1  2032  ax7v2  2033