Result is rationalize(Number)
    which should be preferred.
When Number is an integer, Result is a rational with denominator 1.
When Number is already a rational, Result is identical to Number.
When Number is a float, Result is a rational whose value approximates the value of the float to the accuracy of the float representation. rationalize/2 usually produces more compact rationals that rational/2. Both rationalize/2 and rational/2 produce results that convert back into the original float. rational/2 is usually faster than rationalize/2.
Bounded reals cannot be converted to rationals.
In coroutining mode, if Number is uninstantiated, the call to rationalize/2 is delayed until this variable is instantiated.
Success:
      rationalize(25, 25_1).
      rationalize(1.5, 3_2).
      rationalize(3_4,3_4).
      rationalize(9_12,3_4).
      rationalize(-6, Result).      (gives Result = -6_1)
      rationalize(0.1, Result).     (gives Result = 1_10)
Fail:
      rationalize(1, 2_1).
      rationalize(3, 3).
      rationalize(1, r).
Error:
      rationalize(A, 1_3).                   (Error 4).
      rationalize(4 + 2, 6_1).               (Error 24).
      rationalize(0.9__1.1, X).              (Error 141).