Description: Conjunction in terms of disjunction (De Morgan's law). Theorem *4.5 of WhiteheadRussell p. 120. (Contributed by NM, 3-Jan-1993) (Proof shortened by Wolf Lammen, 3-Nov-2012)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | anor | |- ( ( ph /\ ps ) <-> -. ( -. ph \/ -. ps ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | notnotb | |- ( ( ph /\ ps ) <-> -. -. ( ph /\ ps ) ) |
|
| 2 | ianor | |- ( -. ( ph /\ ps ) <-> ( -. ph \/ -. ps ) ) |
|
| 3 | 1 2 | xchbinx | |- ( ( ph /\ ps ) <-> -. ( -. ph \/ -. ps ) ) |