Description: Complementation reverses inclusion. (Contributed by Andrew Salmon, 15-Jul-2011) (Proof shortened by BJ, 19-Mar-2021)
Ref | Expression | ||
---|---|---|---|
Assertion | complss | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | sscon | |
|
2 | sscon | |
|
3 | ddif | |
|
4 | ddif | |
|
5 | 2 3 4 | 3sstr3g | |
6 | 1 5 | impbii | |