@article{AM2_1976__14_136566,
     author = {Michael Becker},
     title = {Linear approximation processes in locally convex spaces. {I.} {Semigroups} of operators and saturation.},
     journal = {Aequationes mathematicae},
     pages = {73--82},
     publisher = {mathdoc},
     volume = {14},
     year = {1976},
     zbl = {0325.41027},
     url = {http://geodesic.mathdoc.fr/item/AM2_1976__14_136566/}
}