Metamath Proof Explorer

Theorem ex-1st

Description: Example for df-1st . Example by David A. Wheeler. (Contributed by Mario Carneiro, 18-Jun-2015)

Ref Expression
Assertion ex-1st 
|- ( 1st ` <. 3 , 4 >. ) = 3

Proof

Step Hyp Ref Expression
1 3ex 
 |-  3 e. _V
2 4re 
 |-  4 e. RR
3 2 elexi 
 |-  4 e. _V
4 1 3 op1st 
 |-  ( 1st ` <. 3 , 4 >. ) = 3