@article{AIHPA_1997__67_1_1_0,
     author = {Lewis, Roger T. and Siedentop, Heinz and Vugalter, Simeon},
     title = {The essential spectrum of relativistic multi-particle operators},
     journal = {Annales de l'I.H.P. Physique th\'eorique},
     pages = {1--28},
     publisher = {Gauthier-Villars},
     volume = {67},
     number = {1},
     year = {1997},
     mrnumber = {1463002},
     zbl = {0886.35126},
     language = {en},
     url = {http://www.numdam.org/item/AIHPA_1997__67_1_1_0/}
}