Description: The empty set is a function. Theorem 10.3 of Quine p. 65. (Contributed by NM, 7-Apr-1998)
Ref | Expression | ||
---|---|---|---|
Assertion | fun0 | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | 0ss | |
|
2 | 0ex | |
|
3 | 2 2 | funsn | |
4 | funss | |
|
5 | 1 3 4 | mp2 | |