Description: If two propositions are not equivalent, then at least one is true. (Contributed by BJ, 19-Apr-2019) (Proof shortened by Wolf Lammen, 19-Jan-2020)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | nbior | |- ( -. ( ph <-> ps ) -> ( ph \/ ps ) ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | norbi | |- ( -. ( ph \/ ps ) -> ( ph <-> ps ) ) |
|
| 2 | 1 | con1i | |- ( -. ( ph <-> ps ) -> ( ph \/ ps ) ) |