@article{JEDP_1982____A15_0,
     author = {Stein, Elias M.},
     title = {An example of the {Heisenberg} group},
     journal = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {15},
     pages = {1--3},
     publisher = {Ecole polytechnique},
     year = {1982},
     zbl = {0497.35069},
     language = {en},
     url = {http://www.numdam.org/item/JEDP_1982____A15_0/}
}