Description: The ordinal 4 is a natural number. (Contributed by Mario Carneiro, 5-Jan-2016)
Ref | Expression | ||
---|---|---|---|
Assertion | 4onn | |- 4o e. _om |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-4o | |- 4o = suc 3o |
|
2 | 3onn | |- 3o e. _om |
|
3 | peano2 | |- ( 3o e. _om -> suc 3o e. _om ) |
|
4 | 2 3 | ax-mp | |- suc 3o e. _om |
5 | 1 4 | eqeltri | |- 4o e. _om |