Metamath Proof Explorer

Theorem s2len

Description: The length of a doubleton word. (Contributed by Stefan O'Rear, 23-Aug-2015) (Revised by Mario Carneiro, 26-Feb-2016)

Ref Expression
Assertion s2len 
|- ( # ` <" A B "> ) = 2

Proof

Step Hyp Ref Expression
1 df-s2 
 |-  <" A B "> = ( <" A "> ++ <" B "> )
2 s1cli 
 |-  <" A "> e. Word _V
3 s1len 
 |-  ( # ` <" A "> ) = 1
4 1p1e2 
 |-  ( 1 + 1 ) = 2
5 1 2 3 4 cats1len 
 |-  ( # ` <" A B "> ) = 2