Description: A number is equal to the negative of its negative. Theorem I.4 of Apostol p. 18. (Contributed by NM, 12-Jan-2002) (Revised by Mario Carneiro, 27-May-2016)
Ref | Expression | ||
---|---|---|---|
Assertion | negneg | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-neg | |
|
2 | 0cn | |
|
3 | subneg | |
|
4 | 2 3 | mpan | |
5 | 1 4 | eqtrid | |
6 | addid2 | |
|
7 | 5 6 | eqtrd | |