Theorem 19.36-1 1666

Description: Closed form of 19.36i 1665. One direction of Theorem 19.36 of [Margaris] p. 90. The converse holds in classical logic, but does not hold (for all propositions) in intuitionistic logic. (Contributed by Jim Kingdon, 20-Jun-2018.)

Hypothesis

Ref	Expression
19.36-1.1	⊢ Ⅎ𝑥𝜓

Assertion

Ref	Expression
19.36-1	⊢ (∃𝑥(𝜑 → 𝜓) → (∀𝑥𝜑 → 𝜓))

Proof of Theorem 19.36-1

Step	Hyp	Ref	Expression
1		19.35-1 1617	. 2 ⊢ (∃𝑥(𝜑 → 𝜓) → (∀𝑥𝜑 → ∃𝑥𝜓))
2		19.36-1.1	. . 3 ⊢ Ⅎ𝑥𝜓
3	2	19.9 1637	. 2 ⊢ (∃𝑥𝜓 ↔ 𝜓)
4	1, 3	syl6ib 160	1 ⊢ (∃𝑥(𝜑 → 𝜓) → (∀𝑥𝜑 → 𝜓))

Syntax hints:   → wi 4  ∀wal 1346  Ⅎwnf 1453  ∃wex 1485

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-5 1440  ax-gen 1442  ax-ie1 1486  ax-ie2 1487  ax-4 1503  ax-ial 1527

This theorem depends on definitions:  df-bi 116  df-nf 1454

This theorem is referenced by:  vtocl2  2785  vtocl3  2786  spcimgft  2806