4.9 On a $10 \times 10$ grid paper, there are 11 horizontal grid lines and 11 vertical grid lines. A line segment connecting two adjacent nodes on the same straight line is called a "link segment". How many link segments need to be erased at least, so that at most 3 link segments remain at each node?
[Solution] Removing the dotted links in the right figure satisfies the requirements of the problem, and there are 41 dotted links in the figure, so the minimum value required does not exceed 41.

On the other hand, there are 81 internal nodes on the grid paper, each with 4 links. Therefore, at least one link must be erased from each node to meet the requirement. Since each link connects two nodes, at least 41 links must be erased.
In summary, the minimum number of links that need to be erased is 41.