Description: The subsets of an element of a Tarski class belong to the class. (Contributed by FL, 30-Dec-2010) (Revised by Mario Carneiro, 18-Jun-2013)
Ref | Expression | ||
---|---|---|---|
Assertion | tskss |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | elpw2g | ||
2 | 1 | adantl | |
3 | tskpwss | ||
4 | 3 | sseld | |
5 | 2 4 | sylbird | |
6 | 5 | 3impia |