Description: Ordinal 3 is an ordinal number. (Contributed by Mario Carneiro, 5-Jan-2016)
Ref | Expression | ||
---|---|---|---|
Assertion | 3on | ⊢ 3o ∈ On |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-3o | ⊢ 3o = suc 2o | |
2 | 2on | ⊢ 2o ∈ On | |
3 | 2 | onsuci | ⊢ suc 2o ∈ On |
4 | 1 3 | eqeltri | ⊢ 3o ∈ On |