Description: Commutative law for disjunction. Theorem *4.31 of WhiteheadRussell p. 118. (Contributed by NM, 3-Jan-1993) (Proof shortened by Wolf Lammen, 15-Nov-2012)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | orcom | |- ( ( ph \/ ps ) <-> ( ps \/ ph ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | pm1.4 | |- ( ( ph \/ ps ) -> ( ps \/ ph ) ) |
|
| 2 | pm1.4 | |- ( ( ps \/ ph ) -> ( ph \/ ps ) ) |
|
| 3 | 1 2 | impbii | |- ( ( ph \/ ps ) <-> ( ps \/ ph ) ) |