Description: Obsolete version of abf as of 28-Jun-2024. (Contributed by NM, 20-Jan-2012) (Proof modification is discouraged.) (New usage is discouraged.)
| Ref | Expression | ||
|---|---|---|---|
| Hypothesis | abfOLD.1 | |- -. ph |
|
| Assertion | abfOLD | |- { x | ph } = (/) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | abfOLD.1 | |- -. ph |
|
| 2 | ab0 | |- ( { x | ph } = (/) <-> A. x -. ph ) |
|
| 3 | 2 1 | mpgbir | |- { x | ph } = (/) |