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Theorem sb1 1881
Description: One direction of a simplified definition of substitution. The converse requires either a dv condition (sb5 2428) or a non-freeness hypothesis (sb5f 2384). (Contributed by NM, 13-May-1993.)
Assertion
Ref Expression
sb1 ([𝑦 / 𝑥]𝜑 → ∃𝑥(𝑥 = 𝑦𝜑))

Proof of Theorem sb1
StepHypRef Expression
1 df-sb 1879 . 2 ([𝑦 / 𝑥]𝜑 ↔ ((𝑥 = 𝑦𝜑) ∧ ∃𝑥(𝑥 = 𝑦𝜑)))
21simprbi 480 1 ([𝑦 / 𝑥]𝜑 → ∃𝑥(𝑥 = 𝑦𝜑))
Colors of variables: wff setvar class
Syntax hints:  wi 4  wa 384  wex 1702  [wsb 1878
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 1879
This theorem is referenced by:  spsbe  1882  sb4  2354  sb4a  2355  sb4e  2360  sb6  2427  bj-sb4v  32732  bj-sb6  32742  bj-sb3b  32779  wl-sb5nae  33311
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