Theorem sb5rf 1866

Description: Reversed substitution. (Contributed by NM, 3-Feb-2005.) (Proof shortened by Andrew Salmon, 25-May-2011.)

Hypothesis

Ref	Expression
sb5rf.1	⊢ (𝜑 → ∀𝑦𝜑)

Assertion

Ref	Expression
sb5rf	⊢ (𝜑 ↔ ∃𝑦(𝑦 = 𝑥 ∧ [𝑦 / 𝑥]𝜑))

Proof of Theorem sb5rf

Step	Hyp	Ref	Expression
1		sb5rf.1	. . . 4 ⊢ (𝜑 → ∀𝑦𝜑)
2	1	sbid2h 1863	. . 3 ⊢ ([𝑥 / 𝑦][𝑦 / 𝑥]𝜑 ↔ 𝜑)
3		sb1 1780	. . 3 ⊢ ([𝑥 / 𝑦][𝑦 / 𝑥]𝜑 → ∃𝑦(𝑦 = 𝑥 ∧ [𝑦 / 𝑥]𝜑))
4	2, 3	sylbir 135	. 2 ⊢ (𝜑 → ∃𝑦(𝑦 = 𝑥 ∧ [𝑦 / 𝑥]𝜑))
5		stdpc7 1784	. . . 4 ⊢ (𝑦 = 𝑥 → ([𝑦 / 𝑥]𝜑 → 𝜑))
6	5	imp 124	. . 3 ⊢ ((𝑦 = 𝑥 ∧ [𝑦 / 𝑥]𝜑) → 𝜑)
7	1, 6	exlimih 1607	. 2 ⊢ (∃𝑦(𝑦 = 𝑥 ∧ [𝑦 / 𝑥]𝜑) → 𝜑)
8	4, 7	impbii 126	1 ⊢ (𝜑 ↔ ∃𝑦(𝑦 = 𝑥 ∧ [𝑦 / 𝑥]𝜑))

Syntax hints:   → wi 4   ∧ wa 104   ↔ wb 105  ∀wal 1362  ∃wex 1506  [wsb 1776

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-5 1461  ax-gen 1463  ax-ie1 1507  ax-ie2 1508  ax-8 1518  ax-11 1520  ax-4 1524  ax-17 1540  ax-i9 1544  ax-ial 1548

This theorem depends on definitions:  df-bi 117  df-sb 1777

This theorem is referenced by:  2sb5rf  2008  sbelx  2016