On strictly singular operators
Compositio Mathematica, Tome 23 (1971) no. 2, pp. 169-183. 
@article{CM_1971__23_2_169_0,
     author = {Van Dulst, D.},
     title = {On strictly singular operators},
     journal = {Compositio Mathematica},
     pages = {169--183},
     publisher = {Wolters-Noordhoff Publishing},
     volume = {23},
     number = {2},
     year = {1971},
     mrnumber = {288621},
     zbl = {0212.46402},
     language = {en},
     url = {http://www.numdam.org/item/CM_1971__23_2_169_0/}
}
TY  - JOUR
AU  - Van Dulst, D.
TI  - On strictly singular operators
JO  - Compositio Mathematica
PY  - 1971
SP  - 169
EP  - 183
VL  - 23
IS  - 2
PB  - Wolters-Noordhoff Publishing
UR  - http://www.numdam.org/item/CM_1971__23_2_169_0/
LA  - en
ID  - CM_1971__23_2_169_0
ER  - 
%0 Journal Article
%A Van Dulst, D.
%T On strictly singular operators
%J Compositio Mathematica
%D 1971
%P 169-183
%V 23
%N 2
%I Wolters-Noordhoff Publishing
%U http://www.numdam.org/item/CM_1971__23_2_169_0/
%G en
%F CM_1971__23_2_169_0
Van Dulst, D. On strictly singular operators. Compositio Mathematica, Tome 23 (1971) no. 2, pp. 169-183. http://www.numdam.org/item/CM_1971__23_2_169_0/

G.F.C. De Bruyn [1] Riesz properties of linear operators, J. London Math. Soc. 44 (1969), 460-466. | MR | Zbl

D. Van Dulst [2] Perturbation theory and strictly singular operators in locally convex spaces, Studia Math. 38 (1970), 341-372. | MR | Zbl

S. Goldberg [3] Unbounded linear operators, theory and applications, McGraw-Hill, 1966. | MR | Zbl

T. Kato [4] Perturbation theory for nullity, deficiency and other quantities of linear operators, Journ. d'Anal. Math. 6 (1958), 273-322. | MR | Zbl