@article{SF_1989__39_2_134977,
     author = {N. Sauer and J.E. Singleton},
     title = {Evolution operators in empathy with a semi-group.},
     journal = {Semigroup forum},
     pages = {85--94},
     publisher = {mathdoc},
     volume = {39},
     number = {2},
     year = {1989},
     zbl = {0683.47024},
     url = {http://geodesic.mathdoc.fr/item/SF_1989__39_2_134977/}
}