Description: Contraposition. Alternate proof of con3 . This proof is con3ALTVD automatically translated and minimized. (Contributed by Alan Sare, 21-Apr-2013) (Proof modification is discouraged.) (New usage is discouraged.)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | con3ALT2 | |- ( ( ph -> ps ) -> ( -. ps -> -. ph ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | notnotr | |- ( -. -. ph -> ph ) |
|
| 2 | 1 | imim1i | |- ( ( ph -> ps ) -> ( -. -. ph -> ps ) ) |
| 3 | 2 | con1d | |- ( ( ph -> ps ) -> ( -. ps -> -. ph ) ) |