The landlady, landlord, cat, trap, and cheese all take credit for catching the long-tailed rat who is really the only one who knows the truth of the matter.

The theory of the numerical range of a linear operator on an arbitrary normed space had its beginnings around 1960, and during the 1970s the subject has develop

The authors develop various applications, in particular to the study of Banach algebras where the numerical range provides an important link between the algebra