Implementation

Basic Approach

In total it will work like this:

use it +≡
  4 4^ . cr
  bye

Details of the implementation

Here's how we define 4^:

define 4^ +≡
  define square
  : 4^ ( n -- n^4 ) square dup * ;

Here's how we define square:

define square +≡
  : square ( n -- n^2 ) dup * ;

That's it!