Theorem 19.9tOLD 2204

Description: Obsolete proof of 19.9t 2071 as of 6-Oct-2021. (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.) (New usage is discouraged.) (Proof modification is discouraged.)

Assertion

Ref	Expression
19.9tOLD	|- ( F/ x ph -> ( E. x ph <-> ph ) )

Proof of Theorem 19.9tOLD

Step	Hyp	Ref	Expression
1		id 22	. . 3 |- ( F/ x ph -> F/ x ph )
2	1	19.9dOLD 2203	. 2 |- ( F/ x ph -> ( E. x ph -> ph ) )
3		19.8a 2052	. 2 |- ( ph -> E. x ph )
4	2, 3	impbid1 215	1 |- ( F/ x ph -> ( E. x ph <-> ph ) )

Syntax hints:   -> wi 4   <-> wb 196   E.wex 1704   F/wnfOLD 1709

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1722  ax-4 1737  ax-5 1839  ax-6 1888  ax-7 1935  ax-10 2019  ax-12 2047

This theorem depends on definitions:  df-bi 197  df-ex 1705  df-nfOLD 1721

This theorem is referenced by:  19.9OLD  2205  19.21tOLD  2213