Theorem dfsn2ALT 4669

Description: Alternate definition of singleton, based on the (alternate) definition of pair. Definition 5.1 of [TakeutiZaring] p. 15. (Contributed by AV, 12-Jun-2022.) (New usage is discouraged.) (Proof modification is discouraged.)

Assertion

Ref	Expression
dfsn2ALT	⊢ {𝐴} = {𝐴, 𝐴}

Proof of Theorem dfsn2ALT

Dummy variable 𝑥 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		oridm 903	. . 3 ⊢ ((𝑥 = 𝐴 ∨ 𝑥 = 𝐴) ↔ 𝑥 = 𝐴)
2	1	abbii 2812	. 2 ⊢ {𝑥 ∣ (𝑥 = 𝐴 ∨ 𝑥 = 𝐴)} = {𝑥 ∣ 𝑥 = 𝐴}
3		dfpr2 4668	. 2 ⊢ {𝐴, 𝐴} = {𝑥 ∣ (𝑥 = 𝐴 ∨ 𝑥 = 𝐴)}
4		df-sn 4649	. 2 ⊢ {𝐴} = {𝑥 ∣ 𝑥 = 𝐴}
5	2, 3, 4	3eqtr4ri 2779	1 ⊢ {𝐴} = {𝐴, 𝐴}

Syntax hints:   ∨ wo 846   = wceq 1537  {cab 2717  {csn 4648  {cpr 4650

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1793  ax-4 1807  ax-5 1909  ax-6 1967  ax-7 2007  ax-8 2110  ax-9 2118  ax-ext 2711

This theorem depends on definitions:  df-bi 207  df-an 396  df-or 847  df-tru 1540  df-ex 1778  df-sb 2065  df-clab 2718  df-cleq 2732  df-clel 2819  df-v 3490  df-un 3981  df-sn 4649  df-pr 4651

This theorem is referenced by: (None)