Description: If x is not present in ph , then x is not free in ph . (Contributed by Mario Carneiro, 11-Aug-2016) Definition change. (Revised by Wolf Lammen, 12-Sep-2021)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | nfv | |- F/ x ph |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | ax5ea | |- ( E. x ph -> A. x ph ) |
|
| 2 | 1 | nfi | |- F/ x ph |