Description: A natural number is either 0 or a successor. (Contributed by NM, 27-May-1998)
Ref | Expression | ||
---|---|---|---|
Assertion | nn0suc | |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-ne | |
|
2 | nnsuc | |
|
3 | 1 2 | sylan2br | |
4 | 3 | ex | |
5 | 4 | orrd | |