Description: Obsolete version of nfrd as of 23-Nov-2023. (Contributed by Mario Carneiro, 26-Sep-2016) df-nf changed. (Revised by Wolf Lammen, 11-Sep-2021) (Proof modification is discouraged.) (New usage is discouraged.)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | nf5rOLD | |- ( F/ x ph -> ( ph -> A. x ph ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | 19.8a | |- ( ph -> E. x ph ) |
|
| 2 | df-nf | |- ( F/ x ph <-> ( E. x ph -> A. x ph ) ) |
|
| 3 | 2 | biimpi | |- ( F/ x ph -> ( E. x ph -> A. x ph ) ) |
| 4 | 1 3 | syl5 | |- ( F/ x ph -> ( ph -> A. x ph ) ) |