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Theorem sbequ2 1879
Description: An equality theorem for substitution. (Contributed by NM, 16-May-1993.) (Proof shortened by Wolf Lammen, 25-Feb-2018.)
Assertion
Ref Expression
sbequ2 (𝑥 = 𝑦 → ([𝑦 / 𝑥]𝜑𝜑))

Proof of Theorem sbequ2
StepHypRef Expression
1 df-sb 1878 . . 3 ([𝑦 / 𝑥]𝜑 ↔ ((𝑥 = 𝑦𝜑) ∧ ∃𝑥(𝑥 = 𝑦𝜑)))
21simplbi 476 . 2 ([𝑦 / 𝑥]𝜑 → (𝑥 = 𝑦𝜑))
32com12 32 1 (𝑥 = 𝑦 → ([𝑦 / 𝑥]𝜑𝜑))
Colors of variables: wff setvar class
Syntax hints:  wi 4  wa 384  wex 1701  [wsb 1877
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem depends on definitions:  df-bi 197  df-an 386  df-sb 1878
This theorem is referenced by:  stdpc7  1955  sbequ12  2108  dfsb2  2372  sbequi  2374  sbi1  2391  bj-mo3OLD  32530  2pm13.193  38289  2pm13.193VD  38661
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