Description: Addition of positive integers is commutative. (Contributed by NM, 27-Aug-1995) (New usage is discouraged.)
Ref | Expression | ||
---|---|---|---|
Assertion | addcompi | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | pinn | |
|
2 | pinn | |
|
3 | nnacom | |
|
4 | 1 2 3 | syl2an | |
5 | addpiord | |
|
6 | addpiord | |
|
7 | 6 | ancoms | |
8 | 4 5 7 | 3eqtr4d | |
9 | dmaddpi | |
|
10 | 9 | ndmovcom | |
11 | 8 10 | pm2.61i | |