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Theorem elsb4 2423
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 1830 . . 3 𝑦 𝑧𝑤
21sbco2 2403 . 2 ([𝑥 / 𝑦][𝑦 / 𝑤]𝑧𝑤 ↔ [𝑥 / 𝑤]𝑧𝑤)
3 nfv 1830 . . . 4 𝑤 𝑧𝑦
4 elequ2 1991 . . . 4 (𝑤 = 𝑦 → (𝑧𝑤𝑧𝑦))
53, 4sbie 2396 . . 3 ([𝑦 / 𝑤]𝑧𝑤𝑧𝑦)
65sbbii 1874 . 2 ([𝑥 / 𝑦][𝑦 / 𝑤]𝑧𝑤 ↔ [𝑥 / 𝑦]𝑧𝑦)
7 nfv 1830 . . 3 𝑤 𝑧𝑥
8 elequ2 1991 . . 3 (𝑤 = 𝑥 → (𝑧𝑤𝑧𝑥))
97, 8sbie 2396 . 2 ([𝑥 / 𝑤]𝑧𝑤𝑧𝑥)
102, 6, 93bitr3i 289 1 ([𝑥 / 𝑦]𝑧𝑦𝑧𝑥)
Colors of variables: wff setvar class
Syntax hints:  wb 195  [wsb 1867
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1713  ax-4 1728  ax-5 1827  ax-6 1875  ax-7 1922  ax-9 1986  ax-10 2006  ax-11 2021  ax-12 2034  ax-13 2234
This theorem depends on definitions:  df-bi 196  df-or 384  df-an 385  df-tru 1478  df-ex 1696  df-nf 1701  df-sb 1868
This theorem is referenced by:  nfnid  4823
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