Kamsing Nonlaopon. (2012) The operator related to the helmholtz and klein-gordon operator. Khon Kaen University:ม.ป.ท.Kamsing Nonlaopon. 2012. The operator related to the helmholtz and klein-gordon operator. ม.ป.ท.:Khon Kaen University;Kamsing Nonlaopon. The operator related to the helmholtz and klein-gordon operator. ม.ป.ท.:Khon Kaen University, 2012. Print.