@article{AIHPB_1970__6_1_1_0,
     author = {Jirina, Miloslav},
     title = {A simplified proof of the Sevastyanov theorem on branching processes},
     journal = {Annales de l'I.H.P. Probabilit\'es et statistiques},
     publisher = {Gauthier-Villars},
     volume = {6},
     number = {1},
     year = {1970},
     pages = {1-7},
     zbl = {0213.19503},
     mrnumber = {266318},
     language = {en},
     url = {http://www.numdam.org/item/AIHPB_1970__6_1_1_0}
}

Jiřina, Miloslav. A simplified proof of the Sevastyanov theorem on branching processes. Annales de l'I.H.P. Probabilités et statistiques, Volume 6 (1970) no. 1, pp. 1-7. http://www.numdam.org/item/AIHPB_1970__6_1_1_0/