@article{GDZPPN00254914X,
title = {The Numerical Range of a Continuous Mapping of a Normed Space},
journal = {Aequationes mathematicae},
volume = {2},
year = {1969},
pages = {86-93},
zbl = {0162.20101},
url = {http://dml.mathdoc.fr/item/GDZPPN00254914X}
}
BONSALL, F.F.; CAIN, B.E.; SCHNEIDER, H. The Numerical Range of a Continuous Mapping of a Normed Space. Aequationes mathematicae, Tome 2 (1969) pp. 86-93. http://gdmltest.u-ga.fr/item/GDZPPN00254914X/