Result is Number1 / Number2
    which should be preferred for portability.
If both arguments are integers, then the result is of type float by default (coinciding with ISO-Prolog). This can be changed by switching the global flag 'prefer_rationals' to 'on': the result is then of rational type, and therefore precise. In practice, a better way to enforce a rational result is by explicitly converting one or both arguments to a rational before dividing, e.g. Z is rational(X)/Y.
The following table details the behaviour on zero-division, depending on the argument types. The exact result depends on the result's type ability to represent extreme values.
      -3 / 0                        -1.0Inf (negative infinity)
       0 / 0                        arithmetic exception
       3 / 0                         1.0Inf (positive infinity)
      -3.0 / 0.0                    -1.0Inf (negative infinity)
      -0.0 / 0.0                    arithmetic exception
       0.0 / 0.0                    arithmetic exception
       3.0 / 0.0                     1.0Inf (positive infinity)
      -3.0 / -0.0                    1.0Inf (positive infinity)
      -0.0 / -0.0                    arithmetic exception
       0.0 / -0.0                    arithmetic exception
       3.0 / -0.0                   -1.0Inf (negative infinity)
      rational(-3) / rational(0)    representation error
      rational( 0) / rational(0)    arithmetic exception
      rational( 3) / rational(0)    representation error
      breal(-3) / breal(0)          -1.0Inf__-1.0Inf (negative infinity)
      breal( 0) / breal(0)          -1.0Inf__1.0Inf (undefined)
      breal( 3) / breal(0)           1.0Inf__1.0Inf (positive infinity)
   Dividing infinity by infinity yields the same result as 0/0.
In coroutining mode, if Number1 or Number2 are uninstantiated, the call to //3 is delayed until these variables are instantiated.
Success:
    Result is 10 / 2.		% gives Result = 5.0
    Result is 10 / -2.0.	% gives Result = -5.0
    Result is 9 / 12.		% gives Result = 0.75
    % with set_flag(prefer_rationals, on):
    Result is 9 / 12.		% gives Result = 3_4
Error:
    Result is 2/0.              % arithmetic exception