Description: A subset of a well-founded set is well-founded. (Contributed by Mario Carneiro, 17-Nov-2014)
Ref | Expression | ||
---|---|---|---|
Assertion | sswf | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | rankidb | |
|
2 | r1sscl | |
|
3 | 1 2 | sylan | |
4 | r1elwf | |
|
5 | 3 4 | syl | |