Description: Obsolete version of pm2.18 as of 17-Nov-2023. (Contributed by NM, 29-Dec-1992) (Proof modification is discouraged.) (New usage is discouraged.)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | pm2.18OLD | |- ( ( -. ph -> ph ) -> ph ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | pm2.21 | |- ( -. ph -> ( ph -> -. ( -. ph -> ph ) ) ) |
|
| 2 | 1 | a2i | |- ( ( -. ph -> ph ) -> ( -. ph -> -. ( -. ph -> ph ) ) ) |
| 3 | 2 | con4d | |- ( ( -. ph -> ph ) -> ( ( -. ph -> ph ) -> ph ) ) |
| 4 | 3 | pm2.43i | |- ( ( -. ph -> ph ) -> ph ) |