Description: Implication in terms of disjunction. Theorem *4.6 of WhiteheadRussell p. 120. (Contributed by NM, 3-Jan-1993)
Ref | Expression | ||
---|---|---|---|
Assertion | imor | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | notnotb | |
|
2 | 1 | imbi1i | |
3 | df-or | |
|
4 | 2 3 | bitr4i | |