Description: Converse of double negation. Alternate proof of notnotr . This proof is notnotrALTVD automatically translated and minimized. (Contributed by Alan Sare, 21-Apr-2013) (Proof modification is discouraged.) (New usage is discouraged.)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | notnotrALT | |- ( -. -. ph -> ph ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | id | |- ( -. -. ph -> -. -. ph ) |
|
| 2 | pm2.21 | |- ( -. -. ph -> ( -. ph -> -. -. -. ph ) ) |
|
| 3 | 1 2 | mt4d | |- ( -. -. ph -> ph ) |