The following image illustrates the concept:
This loop has 2 simple rules:
- Each red link must be followed by a blue link.
- Each blue link must be followed by a red link.
When we close the loop at node A, we can see that these rules are not obeyed by node A. It has two red links. Therefore, this is a discontinuous loop, with node A being the discontinuity. There can only be a single discontinuity in a discontinuous loop. A loop that violates the rules at multiple locations is not a valid loop.