Supersets for the spectrum of elements in extended Banach algebras
Morteza Seddighin1
Received01 Jun 1987
Revised21 Oct 1987
Abstract
If A is a Banach Algebra with or without an identity, A can be always extended to a Banach algebra A¯ with identity, where A¯ is simply the direct sum of A and C, the algebra of complex numbers. In this note we find supersets for the spectrum of elements of A¯.