Description: Elimination of disjunction by denial of a disjunct. Theorem *2.55 of WhiteheadRussell p. 107. (Contributed by NM, 12-Aug-1994) (Proof shortened by Wolf Lammen, 21-Jul-2012)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | orel1 | |- ( -. ph -> ( ( ph \/ ps ) -> ps ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | pm2.53 | |- ( ( ph \/ ps ) -> ( -. ph -> ps ) ) |
|
| 2 | 1 | com12 | |- ( -. ph -> ( ( ph \/ ps ) -> ps ) ) |