Description: A disjunction is equivalent to a threefold disjunction with single falsehood, analogous to biorf . (Contributed by Alexander van der Vekens, 8-Sep-2017)
Ref | Expression | ||
---|---|---|---|
Hypothesis | 3biorfd.1 | |
|
Assertion | 3bior1fd | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | 3biorfd.1 | |
|
2 | biorf | |
|
3 | 1 2 | syl | |
4 | 3orass | |
|
5 | 3 4 | bitr4di | |