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Theorem difprsnss 4801
Description: Removal of a singleton from an unordered pair. (Contributed by NM, 16-Mar-2006.) (Proof shortened by Andrew Salmon, 29-Jun-2011.)
Assertion
Ref Expression
difprsnss ({𝐴, 𝐵} ∖ {𝐴}) ⊆ {𝐵}

Proof of Theorem difprsnss
Dummy variable 𝑥 is distinct from all other variables.
StepHypRef Expression
1 vex 3476 . . . . 5 𝑥 ∈ V
21elpr 4650 . . . 4 (𝑥 ∈ {𝐴, 𝐵} ↔ (𝑥 = 𝐴𝑥 = 𝐵))
3 velsn 4643 . . . . 5 (𝑥 ∈ {𝐴} ↔ 𝑥 = 𝐴)
43notbii 319 . . . 4 𝑥 ∈ {𝐴} ↔ ¬ 𝑥 = 𝐴)
5 biorf 933 . . . . 5 𝑥 = 𝐴 → (𝑥 = 𝐵 ↔ (𝑥 = 𝐴𝑥 = 𝐵)))
65biimparc 478 . . . 4 (((𝑥 = 𝐴𝑥 = 𝐵) ∧ ¬ 𝑥 = 𝐴) → 𝑥 = 𝐵)
72, 4, 6syl2anb 596 . . 3 ((𝑥 ∈ {𝐴, 𝐵} ∧ ¬ 𝑥 ∈ {𝐴}) → 𝑥 = 𝐵)
8 eldif 3957 . . 3 (𝑥 ∈ ({𝐴, 𝐵} ∖ {𝐴}) ↔ (𝑥 ∈ {𝐴, 𝐵} ∧ ¬ 𝑥 ∈ {𝐴}))
9 velsn 4643 . . 3 (𝑥 ∈ {𝐵} ↔ 𝑥 = 𝐵)
107, 8, 93imtr4i 291 . 2 (𝑥 ∈ ({𝐴, 𝐵} ∖ {𝐴}) → 𝑥 ∈ {𝐵})
1110ssriv 3985 1 ({𝐴, 𝐵} ∖ {𝐴}) ⊆ {𝐵}
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wa 394  wo 843   = wceq 1539  wcel 2104  cdif 3944  wss 3947  {csn 4627  {cpr 4629
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 1911  ax-6 1969  ax-7 2009  ax-8 2106  ax-9 2114  ax-ext 2701
This theorem depends on definitions:  df-bi 206  df-an 395  df-or 844  df-tru 1542  df-ex 1780  df-sb 2066  df-clab 2708  df-cleq 2722  df-clel 2808  df-v 3474  df-dif 3950  df-un 3952  df-in 3954  df-ss 3964  df-sn 4628  df-pr 4630
This theorem is referenced by:  en2other2  10006  pmtrprfv  19362  itg11  25440
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