“…(For reviews of quantum graph, see [1,2].) This system has been applied to various research areas such as scattering theory, nanotechnology on one dimensional graphs [3][4][5][6], quantum chaos [7][8][9], supersymmetric quantum mechanics [10][11][12], extra dimensional models [13][14][15] and so on, due to fascinating structures from boundary conditions. Therefore, the study of boundary conditions on the quantum graph will contribute to the further development of low and high energy physics.…”