Theorem clel5 3649

Description: Alternate definition of class membership: a class 𝑋 is an element of another class 𝐴 iff there is an element of 𝐴 equal to 𝑋. (Contributed by AV, 13-Nov-2020.) Remove use of ax-10 2142, ax-11 2158, and ax-12 2178. (Revised by Steven Nguyen, 19-May-2023.)

Assertion

Ref	Expression
clel5	⊢ (𝑋 ∈ 𝐴 ↔ ∃𝑥 ∈ 𝐴 𝑋 = 𝑥)

Distinct variable groups:   𝑥,𝐴   𝑥,𝑋

Proof of Theorem clel5

Step	Hyp	Ref	Expression
1		risset 3221	. 2 ⊢ (𝑋 ∈ 𝐴 ↔ ∃𝑥 ∈ 𝐴 𝑥 = 𝑋)
2		eqcom 2743	. . 3 ⊢ (𝑥 = 𝑋 ↔ 𝑋 = 𝑥)
3	2	rexbii 3084	. 2 ⊢ (∃𝑥 ∈ 𝐴 𝑥 = 𝑋 ↔ ∃𝑥 ∈ 𝐴 𝑋 = 𝑥)
4	1, 3	bitri 275	1 ⊢ (𝑋 ∈ 𝐴 ↔ ∃𝑥 ∈ 𝐴 𝑋 = 𝑥)

Syntax hints:   ↔ wb 206   = wceq 1540   ∈ wcel 2109  ∃wrex 3061

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 2008  ax-8 2111  ax-9 2119  ax-ext 2708

This theorem depends on definitions:  df-bi 207  df-an 396  df-ex 1780  df-cleq 2728  df-clel 2810  df-rex 3062

This theorem is referenced by:  dfss5  4255  iunid  5041  4fvwrd4  13670  wrdlen1  14577  phisum  16815  symgmov1  19373  n0s0suc  28291  disjunsn  32580  rp-abid  43369