@article{GDZPPN001172336,
title = {Projection Seminorms and the Field of Values of Linear Operators.},
journal = {Numerische Mathematik},
volume = {25},
year = {1975},
pages = {151-162},
zbl = {0323.47003},
url = {http://dml.mathdoc.fr/item/GDZPPN001172336}
}
Martin, R.H. jr.; Lightbourne, J.H. III. Projection Seminorms and the Field of Values of Linear Operators.. Numerische Mathematik, Tome 25 (1975) pp. 151-162. http://gdmltest.u-ga.fr/item/GDZPPN001172336/