Theorem r19.37 2533

Description: Restricted version of one direction of Theorem 19.37 of [Margaris] p. 90. In classical logic the converse would hold if 𝐴 has at least one element, but that is not sufficient in intuitionistic logic. (Contributed by FL, 13-May-2012.) (Revised by Mario Carneiro, 11-Dec-2016.)

Hypothesis

Ref	Expression
r19.37.1	⊢ Ⅎ𝑥𝜑

Assertion

Ref	Expression
r19.37	⊢ (∃𝑥 ∈ 𝐴 (𝜑 → 𝜓) → (𝜑 → ∃𝑥 ∈ 𝐴 𝜓))

Proof of Theorem r19.37

Step	Hyp	Ref	Expression
1		r19.37.1	. . 3 ⊢ Ⅎ𝑥𝜑
2		ax-1 5	. . 3 ⊢ (𝜑 → (𝑥 ∈ 𝐴 → 𝜑))
3	1, 2	ralrimi 2456	. 2 ⊢ (𝜑 → ∀𝑥 ∈ 𝐴 𝜑)
4		r19.35-1 2531	. 2 ⊢ (∃𝑥 ∈ 𝐴 (𝜑 → 𝜓) → (∀𝑥 ∈ 𝐴 𝜑 → ∃𝑥 ∈ 𝐴 𝜓))
5	3, 4	syl5 32	1 ⊢ (∃𝑥 ∈ 𝐴 (𝜑 → 𝜓) → (𝜑 → ∃𝑥 ∈ 𝐴 𝜓))

Syntax hints:   → wi 4  Ⅎwnf 1401   ∈ wcel 1445  ∀wral 2370  ∃wrex 2371

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-5 1388  ax-gen 1390  ax-ie1 1434  ax-ie2 1435  ax-4 1452  ax-ial 1479

This theorem depends on definitions:  df-bi 116  df-nf 1402  df-ral 2375  df-rex 2376

This theorem is referenced by:  r19.37av  2534