@article{MS2_1968__22_166044,
     author = {Heinz Langer},
     title = {\"Uber die schwache {Stabilt\"at} linearer {Differentialgleichungen} mit periodischen {Koeffizienten.}},
     journal = {Mathematica Scandinavica},
     pages = {203--208},
     publisher = {mathdoc},
     volume = {22},
     year = {1968},
     zbl = {0175.38102},
     url = {http://geodesic.mathdoc.fr/item/MS2_1968__22_166044/}
}