For $$x \neq -1$$, define $$\frac{x - 1}{x + 2}$$, then $$f(x) = \frac{f(x) - f(y)}{1+f(x)f(y)}$$

A

$$\frac{x+y}{1-xy}$$

B

$$\frac{x-y}{1+xy}$$

C

$$\frac{x+y}{x-y}$$

D

1