Description: Obsolete version of falnorfal as of 17-Dec-2023. (Contributed by Remi, 25-Oct-2023) (Proof modification is discouraged.) (New usage is discouraged.)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | falnorfalOLD | |- ( ( F. -\/ F. ) <-> T. ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | df-nor | |- ( ( F. -\/ F. ) <-> -. ( F. \/ F. ) ) |
|
| 2 | notfal | |- ( -. F. <-> T. ) |
|
| 3 | 2 | bicomi | |- ( T. <-> -. F. ) |
| 4 | falorfal | |- ( ( F. \/ F. ) <-> F. ) |
|
| 5 | 4 | bicomi | |- ( F. <-> ( F. \/ F. ) ) |
| 6 | 3 5 | xchbinx | |- ( T. <-> -. ( F. \/ F. ) ) |
| 7 | 6 | bicomi | |- ( -. ( F. \/ F. ) <-> T. ) |
| 8 | 1 7 | bitri | |- ( ( F. -\/ F. ) <-> T. ) |