In this case the left and right limits are different. From the left, the value is 16, while from the right, the value is 13. When the left and right limits disagree, we say that the limit does not exist, since there is no single limit. We've approached limits from a geometric and a numeric point of view. Lets now address the symbolic side.
Maple is able to compute the left limit, the right limit, and the limit of a function.
To find a limit just type the function and target value.