Say you have a set of points and joining lines as show below:
In this diagram of triangles, T-(or Y-like) junctions are at D, F, and E.
At vertex F for example, there is a triangle FDE, but no line FJ. If there was a line FJ, then there would be no T junction at F. Two triangles would be formed instead out of triangle-ACJ as tri-AFC and tri-FCJ.
How do you find the vertices that form "T" (or Y-like) junctions?