设 f(x)={x/y,if y≠0 and y ∣ x,↑,else. f(x) = \left\{\begin{array}{ll} x / y, & \text{if } y \neq 0 \text{ and } y~|~x,\\ \uparrow, & \text{else.} \end{array}\right. f(x)={x/y,↑,if y≠0 and y ∣ x,else. 证明：f∈RFf \in \mathcal{RF}f∈RF。
f(x)=μz.(zy=x) and (y≠0)=μz.(x−¨zy)⋅Ny f(x) = \mu z. (zy =x) \text{ and } (y \neq 0) = \mu z.(x \ddot{-}zy)\cdot Ny f(x)=μz.(zy=x) and (y≠0)=μz.(x−¨zy)⋅Ny