Theorem 19.9t 2227

Description: A closed version of 19.9 2228. (Contributed by NM, 13-May-1993.) (Revised by Mario Carneiro, 24-Sep-2016.) (Proof shortened by Wolf Lammen, 30-Dec-2017.) (Proof shortened by Wolf Lammen, 14-Jul-2020.)

Assertion

Ref	Expression
19.9t	⊢ (Ⅎ𝑥𝜑 → (∃𝑥𝜑 ↔ 𝜑))

Proof of Theorem 19.9t

Step	Hyp	Ref	Expression
1		id 22	. . 3 ⊢ (Ⅎ𝑥𝜑 → Ⅎ𝑥𝜑)
2	1	19.9d 2225	. 2 ⊢ (Ⅎ𝑥𝜑 → (∃𝑥𝜑 → 𝜑))
3		19.8a 2206	. 2 ⊢ (𝜑 → ∃𝑥𝜑)
4	2, 3	impbid1 215	1 ⊢ (Ⅎ𝑥𝜑 → (∃𝑥𝜑 ↔ 𝜑))

Syntax hints:   → wi 4   ↔ wb 196  ∃wex 1852  Ⅎwnf 1856

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1870  ax-4 1885  ax-5 1991  ax-6 2057  ax-7 2093  ax-12 2203

This theorem depends on definitions:  df-bi 197  df-ex 1853  df-nf 1858

This theorem is referenced by:  19.9  2228  19.21t  2229  19.21tOLDOLD  2230  spimt  2415  sbft  2526  vtoclegft  3431  bj-cbv3tb  33048  bj-spimtv  33055  bj-sbftv  33099  bj-equsal1t  33144  bj-19.21t  33152  19.9alt  34774