Here's the question you clicked on:
here R(x,y) basically means a function which consists of both x and y variables in which the variable x and y can't be seprated like R(x,y) = x^2 +y^2+9xy....he has used R(x,y) because function to be represented is F(x+y) which could inseprable terms of xy...
is it ok @across , but the person who has wriiten that has surely made that difficult