The group of invertible elements in a Banach algebra
The holomorphic functional calculus as an operational calculus
The monogenic functional calculus
A study is made of a symmetric functional calculus for a system of bounded linear operators acting on a Banach space. Finite real linear combinations of the operators have real spectra, but the operators do not necessarily commute with each other. Analytic functions of the operators are formed by using functions taking their values in a Clifford algebra.
The Relative Spectrum of Elements in a Real Banach Algebra.
The Taylor spectrum and quotient Banach spaces