Description: The preimage of a subset is a subset of the preimage. (Contributed by Brendan Leahy, 23-Sep-2017)
Ref | Expression | ||
---|---|---|---|
Assertion | sspreima | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | inpreima | |
|
2 | df-ss | |
|
3 | 2 | biimpi | |
4 | 3 | imaeq2d | |
5 | 1 4 | sylan9req | |
6 | df-ss | |
|
7 | 5 6 | sylibr | |