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| Mirrors > Home > ILE Home > Th. List > Mathboxes > nnnotnotr | Unicode version | ||
| Description: Double negation of double negation elimination. Suggested by an online post by Martin Escardo. Although this statement resembles nnexmid 862, it can be proved with reference only to implication and negation (that is, without use of disjunction). (Contributed by Jim Kingdon, 21-Oct-2024.) |
| Ref | Expression |
|---|---|
| nnnotnotr |
  
   |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | conax1 663 |
. 2
| |
| 2 | pm2.24 630 |
. . 3
| |
| 3 | 2 | con3i 641 |
. 2
|
| 4 | 1, 3 | pm2.65i 648 |
1
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| Colors of variables: wff set class |
| Syntax hints: wn 3
wi 4 |
| This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-in1 623 ax-in2 624 |
| This theorem is referenced by: (None) |
| Copyright terms: Public domain | W3C validator |