Result is sgn(Number)
    which should be preferred for portability.
sgn/2 gives the integer -1 if Number is negative, 0 if it is zero and 1 if it is greater than zero. It is always true that
    X =:= sgn(X) * abs(X)
   Caution: this operation does not distinguish between +0.0 and -0.0.
   See copysign/3 for an alternative.
In coroutining mode, if Number is uninstantiated, the call to sgn/2 is delayed until this variable is instantiated.
    Result is sgn(42).		% gives Result = 1
    Result is sgn(-5).		% gives Result = -1
    Result is sgn(-6.2).	% gives Result = -1
    Result is sgn(0.0).		% gives Result = 0
    Result is sgn(-0.0).	% gives Result = 0