Description: A nonzero square is positive. Theorem I.20 of Apostol p. 20. (Contributed by NM, 6-May-1999) (Proof shortened by Mario Carneiro, 27-May-2016)
Ref | Expression | ||
---|---|---|---|
Assertion | msqgt0 | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | id | |
|
2 | 0red | |
|
3 | 1 2 | lttri2d | |
4 | 3 | biimpa | |
5 | mullt0 | |
|
6 | 5 | anidms | |
7 | mulgt0 | |
|
8 | 7 | anidms | |
9 | 6 8 | jaodan | |
10 | 4 9 | syldan | |