@article{IM_1967__4_141895,
     author = {H. TRIEBEL},
     title = {\"Uber die {Verteilung} der {Approximationszahlen} kompakter {Operatoren} in {Sobolev-Besov-R\"aumen.}},
     journal = {Inventiones mathematicae},
     pages = {275--293},
     publisher = {mathdoc},
     volume = {4},
     year = {1967},
     zbl = {0165.14501},
     url = {http://geodesic.mathdoc.fr/item/IM_1967__4_141895/}
}