“…The graph F u,N is connected exactly for N ≤ 4, and it is a tree exactly for N = 2, 4. Using the graph F 1,2 and F 1,3 , we have constructed continued fractions called F 1,2 -continued fractions [7] and F 1,3 -continued fractions [4], respectively. The graphs F u,N and F N −u,N are isomorphic under the map v → −v for each vertex v of F u,N .…”