@article{700970,
     title = {The boundary of the spectrum of a linear Operatoro},
     booktitle = {General Topology and its Relations to Modern Analysis and Algebra},
     series = {GDML\_Books},
     publisher = {Academia Publishing House of the Czechoslovak Academy of Sciences},
     address = {Praha},
     year = {1962},
     pages = {347-350},
     mrnumber = {MR0173949},
     zbl = {0111.30802},
     url = {http://dml.mathdoc.fr/item/700970}
}

Taylor, A. E. The boundary of the spectrum of a linear Operatoro, dans General Topology and its Relations to Modern Analysis and Algebra, GDML_Books,  (1962), pp. 347-350. http://gdmltest.u-ga.fr/item/700970/