@article{IM_1973__20_142214,
     author = {J. Sj\"ostrand and J.J. Duistermaat},
     title = {A {Global} {Construction} for {Pseudo-Differential} {Operators} with {Non-Involutive} {Characteristcs.}},
     journal = {Inventiones mathematicae},
     pages = {209--226},
     publisher = {mathdoc},
     volume = {20},
     year = {1973},
     zbl = {0282.35071},
     url = {http://geodesic.mathdoc.fr/item/IM_1973__20_142214/}
}