Description: Contraposition. Theorem *2.15 of WhiteheadRussell p. 102. Its associated inference is con1i . (Contributed by NM, 29-Dec-1992) (Proof shortened by Wolf Lammen, 12-Feb-2013)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | con1 | |- ( ( -. ph -> ps ) -> ( -. ps -> ph ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | id | |- ( ( -. ph -> ps ) -> ( -. ph -> ps ) ) |
|
| 2 | 1 | con1d | |- ( ( -. ph -> ps ) -> ( -. ps -> ph ) ) |