6.1.0400
2OVER
two-over
CORE
 
( x1 x2 x3 x4 -- x1 x2 x3 x4 x1 x2 )

Copy cell pair x1 x2 to the top of the stack.

Testing:
T{ 1 2 3 4 2OVER -> 1 2 3 4 1 2 }T