Theorem iseqsetv-cleq 2805

Description: Alternate proof of iseqsetv-clel 2819. The expression ∃𝑥𝑥 = 𝐴 does not depend on a particular choice of the set variable. The proof here avoids df-clab 2714, df-clel 2815 and ax-8 2110, but instead is based on ax-9 2118, ax-ext 2707 and df-cleq 2728. In particular it still accepts 𝑥 ∈ 𝐴 being a primitive syntax term, not assuming any specific semantics (like elementhood in some form).

Use it in contexts where you want to avoid df-clab 2714, or you need df-cleq 2728 anyway. See the alternative version , not using df-cleq 2728 or ax-ext 2707 or ax-9 2118. (Contributed by Wolf Lammen, 6-Aug-2025.) (Proof modification is discouraged.)

Assertion

Ref	Expression
iseqsetv-cleq	⊢ (∃𝑥 𝑥 = 𝐴 ↔ ∃𝑦 𝑦 = 𝐴)

Distinct variable groups:   𝑥,𝐴   𝑦,𝐴

Proof of Theorem iseqsetv-cleq

Dummy variable 𝑧 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		iseqsetvlem 2804	. 2 ⊢ (∃𝑥 𝑥 = 𝐴 ↔ ∃𝑧 𝑧 = 𝐴)
2		iseqsetvlem 2804	. 2 ⊢ (∃𝑦 𝑦 = 𝐴 ↔ ∃𝑧 𝑧 = 𝐴)
3	1, 2	bitr4i 278	1 ⊢ (∃𝑥 𝑥 = 𝐴 ↔ ∃𝑦 𝑦 = 𝐴)

Syntax hints:   ↔ wb 206   = wceq 1540  ∃wex 1779

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1795  ax-4 1809  ax-5 1910  ax-6 1967  ax-7 2007  ax-9 2118  ax-ext 2707

This theorem depends on definitions:  df-bi 207  df-an 396  df-ex 1780  df-cleq 2728

This theorem is referenced by:  clelab  2886