Description: The undefined value generated from a set is not a member of the set. (Contributed by NM, 15-Sep-2011)
Ref | Expression | ||
---|---|---|---|
Assertion | undefnel | |- ( S e. V -> ( Undef ` S ) e/ S ) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | undefnel2 | |- ( S e. V -> -. ( Undef ` S ) e. S ) |
|
2 | df-nel | |- ( ( Undef ` S ) e/ S <-> -. ( Undef ` S ) e. S ) |
|
3 | 1 2 | sylibr | |- ( S e. V -> ( Undef ` S ) e/ S ) |