Availability:Arithmetic function (see is/2) 
[ISO]+IntExpr1 >> +IntExpr2Bitwise shift IntExpr1 by IntExpr2 bits to the 
right. The ISO standard dictates shifting a negative value is
implementation defined. SWI-Prolog defines shifting negative 
integers to be defined as -(-Int>>Shift). Shifting 
positive integers by more than their size results in 0 (zero). Shifting 
negative integers by more then their size results in -1. I.e.,
A is -3464 >> 100 binds A to -1. If IntExpr2 
is negative, a right shift (see >>/2) 
is performed with the negated value of IntExpr2.