Description: A contraposition deduction. (Contributed by NM, 19-Aug-1993)
| Ref | Expression | ||
|---|---|---|---|
| Hypothesis | con2d.1 | |- ( ph -> ( ps -> -. ch ) ) |
|
| Assertion | con2d | |- ( ph -> ( ch -> -. ps ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | con2d.1 | |- ( ph -> ( ps -> -. ch ) ) |
|
| 2 | notnotr | |- ( -. -. ps -> ps ) |
|
| 3 | 2 1 | syl5 | |- ( ph -> ( -. -. ps -> -. ch ) ) |
| 4 | 3 | con4d | |- ( ph -> ( ch -> -. ps ) ) |