Note that in orderfor lim
ðx;yÞ!ðx0;y0Þ
f ðx; yÞ to exist, it must have the same value regardless of the
approach of ðx; yÞ to ðx0; y0Þ. It follows that if two different approaches give different values, the
limit cannot exist (see Problem 6.7). This implies, as in the case of functions of one variable, that if a
limit exists it is unique.
The concept of one-sided limits for functions of one variable is easily extended to functions of more
than one variable.