Description: Elimination of an existential quantifier, using implicit substitution. (Contributed by NM, 2-Mar-1995) Avoid ax-12 . (Revised by Gino Giotto, 12-Oct-2024) (Proof shortened by Wolf Lammen, 22-Jan-2025)
Ref | Expression | ||
---|---|---|---|
Hypotheses | ceqsexv.1 | |- A e. _V |
|
ceqsexv.2 | |- ( x = A -> ( ph <-> ps ) ) |
||
Assertion | ceqsexv | |- ( E. x ( x = A /\ ph ) <-> ps ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ceqsexv.1 | |- A e. _V |
|
2 | ceqsexv.2 | |- ( x = A -> ( ph <-> ps ) ) |
|
3 | alinexa | |- ( A. x ( x = A -> -. ph ) <-> -. E. x ( x = A /\ ph ) ) |
|
4 | 2 | notbid | |- ( x = A -> ( -. ph <-> -. ps ) ) |
5 | 1 4 | ceqsalv | |- ( A. x ( x = A -> -. ph ) <-> -. ps ) |
6 | 3 5 | bitr3i | |- ( -. E. x ( x = A /\ ph ) <-> -. ps ) |
7 | 6 | con4bii | |- ( E. x ( x = A /\ ph ) <-> ps ) |