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Theorem difprsnss 4470
 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 3339 . . . . 5 𝑥 ∈ V
21elpr 4339 . . . 4 (𝑥 ∈ {𝐴, 𝐵} ↔ (𝑥 = 𝐴𝑥 = 𝐵))
3 velsn 4333 . . . . 5 (𝑥 ∈ {𝐴} ↔ 𝑥 = 𝐴)
43notbii 309 . . . 4 𝑥 ∈ {𝐴} ↔ ¬ 𝑥 = 𝐴)
5 biorf 419 . . . . 5 𝑥 = 𝐴 → (𝑥 = 𝐵 ↔ (𝑥 = 𝐴𝑥 = 𝐵)))
65biimparc 505 . . . 4 (((𝑥 = 𝐴𝑥 = 𝐵) ∧ ¬ 𝑥 = 𝐴) → 𝑥 = 𝐵)
72, 4, 6syl2anb 497 . . 3 ((𝑥 ∈ {𝐴, 𝐵} ∧ ¬ 𝑥 ∈ {𝐴}) → 𝑥 = 𝐵)
8 eldif 3721 . . 3 (𝑥 ∈ ({𝐴, 𝐵} ∖ {𝐴}) ↔ (𝑥 ∈ {𝐴, 𝐵} ∧ ¬ 𝑥 ∈ {𝐴}))
9 velsn 4333 . . 3 (𝑥 ∈ {𝐵} ↔ 𝑥 = 𝐵)
107, 8, 93imtr4i 281 . 2 (𝑥 ∈ ({𝐴, 𝐵} ∖ {𝐴}) → 𝑥 ∈ {𝐵})
1110ssriv 3744 1 ({𝐴, 𝐵} ∖ {𝐴}) ⊆ {𝐵}
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3   ∨ wo 382   ∧ wa 383   = wceq 1628   ∈ wcel 2135   ∖ cdif 3708   ⊆ wss 3711  {csn 4317  {cpr 4319 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1867  ax-4 1882  ax-5 1984  ax-6 2050  ax-7 2086  ax-9 2144  ax-10 2164  ax-11 2179  ax-12 2192  ax-13 2387  ax-ext 2736 This theorem depends on definitions:  df-bi 197  df-or 384  df-an 385  df-tru 1631  df-ex 1850  df-nf 1855  df-sb 2043  df-clab 2743  df-cleq 2749  df-clel 2752  df-nfc 2887  df-v 3338  df-dif 3714  df-un 3716  df-in 3718  df-ss 3725  df-sn 4318  df-pr 4320 This theorem is referenced by:  en2other2  9018  pmtrprfv  18069  itg11  23653
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