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Theorem dfsn2ALT 4568
 Description: Alternate definition of singleton, based on the (alternate) definition of unordered 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.
StepHypRef Expression
1 oridm 902 . . 3 ((𝑥 = 𝐴𝑥 = 𝐴) ↔ 𝑥 = 𝐴)
21abbii 2889 . 2 {𝑥 ∣ (𝑥 = 𝐴𝑥 = 𝐴)} = {𝑥𝑥 = 𝐴}
3 dfpr2 4567 . 2 {𝐴, 𝐴} = {𝑥 ∣ (𝑥 = 𝐴𝑥 = 𝐴)}
4 df-sn 4549 . 2 {𝐴} = {𝑥𝑥 = 𝐴}
52, 3, 43eqtr4ri 2858 1 {𝐴} = {𝐴, 𝐴}
 Colors of variables: wff setvar class Syntax hints:   ∨ wo 844   = wceq 1538  {cab 2802  {csn 4548  {cpr 4550 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1797  ax-4 1811  ax-5 1912  ax-6 1971  ax-7 2016  ax-8 2117  ax-9 2125  ax-ext 2796 This theorem depends on definitions:  df-bi 210  df-an 400  df-or 845  df-tru 1541  df-ex 1782  df-sb 2071  df-clab 2803  df-cleq 2817  df-clel 2896  df-v 3481  df-un 3923  df-sn 4549  df-pr 4551 This theorem is referenced by: (None)
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