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