I'm working on a section on limits ofmultivariate functions. In looking through the examples, for f(x,y) = (4-xy) / (x^2 + 3y^2), it is said that this is a rational function and thus continuous, the next question however, f(x,y) = y^4 / (x^4 + 3y^4), goes into analysis of the limit. Isn't the latter one also a rational function?