@article{PORMA_1992__49_3_115791,
     author = {Schmeelk, John and Takaci, Arpad},
     title = {Ultra annihilation and creation operators},
     journal = {Portugaliae mathematica},
     pages = {263--279},
     publisher = {mathdoc},
     volume = {49},
     number = {3},
     year = {1992},
     mrnumber = {1201291},
     zbl = {0771.46040},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1992__49_3_115791/}
}