Description: Equality theorem for proper subclass. (Contributed by NM, 7-Feb-1996)
Ref | Expression | ||
---|---|---|---|
Assertion | psseq1 | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | sseq1 | |
|
2 | neeq1 | |
|
3 | 1 2 | anbi12d | |
4 | df-pss | |
|
5 | df-pss | |
|
6 | 3 4 5 | 3bitr4g | |