In many practical situations, we must compute the value of an if-then expression f(x) defined as “if c(x) ≥ 0 then f+(x) else f−(x)”, where f+(x), f−(x), and c(x) are computable functions. The value f(x) cannot be computed directly, since in general, it is not possible to check whether a given real number c(x) is non-negative or non-positive. Similarly, it is not possible to compute the value f...