@article{MS2_1971__28_166168,
     author = {Henrik Stetkaer},
     title = {Invariant {Pseudo-Differential} {Operators.}},
     journal = {Mathematica Scandinavica},
     pages = {105--123},
     publisher = {mathdoc},
     volume = {28},
     year = {1971},
     zbl = {0226.58010},
     url = {http://geodesic.mathdoc.fr/item/MS2_1971__28_166168/}
}