I am currently working through Tiernan's paper, "An efficient search algorithm to find the elementary circuits of a graph" (published 1970), and I am stuck on point 3 of the following excerpt:
The algorithm is named EC for "elementary circuit." The function blocks of EC are denoted EC1, EC2, etc. EC requires that there be assigned to the vertices, in any order, the integer designators 1, 2, .-., N. The algorithm utilizes two principal arrays in addition to that describing the graph. The first is a one-dimensional array, P, containing the vertices of an elementary path. The second is a two-dimensional array, H, and is initially zeroed. Elementary path building in P is the basic process of EC. The first path is started as vertex 1. A path is extended from its end, one arc at a time, with three conditions checked before a tentative extension is performed:
- The extension vertex cannot be in P.
- The extension vertex value must be larger than that of the first vertex of P.
- The extension vertex cannot be closed to the last vertex in P. H contains the list of vertices closed to each vertex.
What does Tiernan mean by point 3? I've tried googling the term "closed to [some vertex]", but the results were not entirely helpful.