Description: The class of all subsets of a class is closed under class difference. (Contributed by RP, 3-Jan-2020)
Ref | Expression | ||
---|---|---|---|
Hypothesis | ssficl.a | ||
Assertion | ssdifcl |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ssficl.a | ||
2 | vex | ||
3 | 2 | difexi | |
4 | sseq1 | ||
5 | sseq1 | ||
6 | sseq1 | ||
7 | ssdifss | ||
8 | 7 | adantr | |
9 | 1 3 4 5 6 8 | cllem0 |