Metamath Proof Explorer

Theorem hash3

Description: Size of a finite ordinal. (Contributed by Mario Carneiro, 5-Jan-2016)

Ref Expression
Assertion hash3 
|- ( # ` 3o ) = 3

Proof

Step Hyp Ref Expression
1 2onn 
 |-  2o e. _om
2 df-3o 
 |-  3o = suc 2o
3 hash2 
 |-  ( # ` 2o ) = 2
4 2p1e3 
 |-  ( 2 + 1 ) = 3
5 1 2 3 4 hashp1i 
 |-  ( # ` 3o ) = 3