Description: Obsolete version of 19.3v as of 20-Oct-2023. (Contributed by Anthony Hart, 13-Sep-2011) Remove dependency on ax-7 . (Revised by Wolf Lammen, 4-Dec-2017) (Proof modification is discouraged.) (New usage is discouraged.)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | 19.3vOLD | |- ( A. x ph <-> ph ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | alex | |- ( A. x ph <-> -. E. x -. ph ) |
|
| 2 | 19.9v | |- ( E. x -. ph <-> -. ph ) |
|
| 3 | 2 | con2bii | |- ( ph <-> -. E. x -. ph ) |
| 4 | 1 3 | bitr4i | |- ( A. x ph <-> ph ) |