@article{MAN_1989__284_4_164572,
     author = {Klaus-J. Engel},
     title = {Polynomial operator matrices as semigroup generators: the 2 x 2 case.},
     journal = {Mathematische Annalen},
     pages = {563--576},
     publisher = {mathdoc},
     volume = {284},
     number = {4},
     year = {1989},
     zbl = {0652.34013},
     url = {http://geodesic.mathdoc.fr/item/MAN_1989__284_4_164572/}
}