Description: Commutative law for conjunction. Theorem *4.3 of WhiteheadRussell p. 118. (Contributed by NM, 25-Jun-1998) (Proof shortened by Wolf Lammen, 4-Nov-2012)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | ancom | |- ( ( ph /\ ps ) <-> ( ps /\ ph ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | pm3.22 | |- ( ( ph /\ ps ) -> ( ps /\ ph ) ) |
|
| 2 | pm3.22 | |- ( ( ps /\ ph ) -> ( ph /\ ps ) ) |
|
| 3 | 1 2 | impbii | |- ( ( ph /\ ps ) <-> ( ps /\ ph ) ) |