Description: 7 times 4 equals 28. (Contributed by Mario Carneiro, 19-Apr-2015)
| Ref | Expression | ||
|---|---|---|---|
| Assertion | 7t4e28 | |- ( 7 x. 4 ) = ; 2 8 |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | 7nn0 | |- 7 e. NN0 |
|
| 2 | 3nn0 | |- 3 e. NN0 |
|
| 3 | df-4 | |- 4 = ( 3 + 1 ) |
|
| 4 | 7t3e21 | |- ( 7 x. 3 ) = ; 2 1 |
|
| 5 | 2nn0 | |- 2 e. NN0 |
|
| 6 | 1nn0 | |- 1 e. NN0 |
|
| 7 | eqid | |- ; 2 1 = ; 2 1 |
|
| 8 | 7cn | |- 7 e. CC |
|
| 9 | ax-1cn | |- 1 e. CC |
|
| 10 | 7p1e8 | |- ( 7 + 1 ) = 8 |
|
| 11 | 8 9 10 | addcomli | |- ( 1 + 7 ) = 8 |
| 12 | 5 6 1 7 11 | decaddi | |- ( ; 2 1 + 7 ) = ; 2 8 |
| 13 | 1 2 3 4 12 | 4t3lem | |- ( 7 x. 4 ) = ; 2 8 |