ABSTRACT
Holomorphic functional calculus. This is an extended version of the functional calculus for entire functions. If A is again a bounded operator in a Banach space and f ( z ) is a function holomorphic in a neighborhood of the spectrum σ(Α ), then one sets
where the integral is taken over a contour lying in the domain where / is holomorphic and surround ing the spectrum σ(Α) counterclockwise.
