Description: A short form of the axiom B of modal logic using only primitive symbols ( -> , -. , A. ). (Contributed by BJ, 4-Apr-2021) (Proof modification is discouraged.)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | bj-modalb | |- ( -. ph -> A. x -. A. x ph ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | axc7 | |- ( -. A. x -. A. x ph -> ph ) |
|
| 2 | 1 | con1i | |- ( -. ph -> A. x -. A. x ph ) |