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Theorem elsb4 2434
 Description: Substitution applied to an atomic membership wff. (Contributed by Rodolfo Medina, 3-Apr-2010.) (Proof shortened by Andrew Salmon, 14-Jun-2011.)
Assertion
Ref Expression
elsb4 ([𝑥 / 𝑦]𝑧𝑦𝑧𝑥)
Distinct variable group:   𝑦,𝑧

Proof of Theorem elsb4
Dummy variable 𝑤 is distinct from all other variables.
StepHypRef Expression
1 nfv 1840 . . 3 𝑦 𝑧𝑤
21sbco2 2414 . 2 ([𝑥 / 𝑦][𝑦 / 𝑤]𝑧𝑤 ↔ [𝑥 / 𝑤]𝑧𝑤)
3 nfv 1840 . . . 4 𝑤 𝑧𝑦
4 elequ2 2001 . . . 4 (𝑤 = 𝑦 → (𝑧𝑤𝑧𝑦))
53, 4sbie 2407 . . 3 ([𝑦 / 𝑤]𝑧𝑤𝑧𝑦)
65sbbii 1884 . 2 ([𝑥 / 𝑦][𝑦 / 𝑤]𝑧𝑤 ↔ [𝑥 / 𝑦]𝑧𝑦)
7 nfv 1840 . . 3 𝑤 𝑧𝑥
8 elequ2 2001 . . 3 (𝑤 = 𝑥 → (𝑧𝑤𝑧𝑥))
97, 8sbie 2407 . 2 ([𝑥 / 𝑤]𝑧𝑤𝑧𝑥)
102, 6, 93bitr3i 290 1 ([𝑥 / 𝑦]𝑧𝑦𝑧𝑥)
 Colors of variables: wff setvar class Syntax hints:   ↔ wb 196  [wsb 1877 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1719  ax-4 1734  ax-5 1836  ax-6 1885  ax-7 1932  ax-9 1996  ax-10 2016  ax-11 2031  ax-12 2044  ax-13 2245 This theorem depends on definitions:  df-bi 197  df-or 385  df-an 386  df-tru 1483  df-ex 1702  df-nf 1707  df-sb 1878 This theorem is referenced by:  nfnid  4867
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