Victor Chepoi Bertrand Estellon Karim Nouioua Yann Vaxès Mixed covering of trees and the augmentation problem with odd diameter constraints. 405-408 2005 22 Electronic Notes in Discrete Mathematics http://dx.doi.org/10.1016/j.endm.2005.06.068 db/journals/endm/endm22.html#ChepoiENV05