Function: _>>=_
Class: symbolic_operators
Description: 
 (*small, small):small:parens	        $1 >>= $(2)
 (*int, small):int:parens	         $1 = shifti($1, -$(2))
 (*mp, small):mp:parens	                 $1 = mpshift($1, -$(2))
 (*gen, small):mp:parens	         $1 = gshift($1, -$(2))

