2/ 2- 2>R
2/ ( a -- a/2 )  
ansi .6.1.0330 <CORE>
divides the value by two - but it does actually use a shift1 to be faster 
 simulate:
  : 2/ 2 / ; ( canonic) : 2/ 1 RSHIFT ; ( usual)

reference: p4_two_slash in ../src/core.c:0419, export CO 2/