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F. F. Bonsal and J. Duncan, “Numerical Ranges of Operators on Normed Spaces and Elements of Normed Algebras,” Cambridge University Press, Cambridge, 1971.

has been cited by the following article:

• TITLE: On the Generality of Orthogonal Projections and e-Projections in Banach Algebras

  AUTHORS: Mohammad Sadegh Asgari, Seyedeh Sara Karimizad, Hamidreza Rahimi

  KEYWORDS: Generalized Orthogonal Projection; Orthogonal Projection; Generalized e-Projection; e-Projection

  JOURNAL NAME: Advances in Pure Mathematics, Vol.2 No.5, September 26, 2012

  ABSTRACT: In this paper we develop the orthogonal projections and e-projections in Banach algebras. We prove some necessary and sufficient conditions for them and their spectrums. We also show that the sum of two generalized orthogonal projections u and v is a generalized orthogonal projection if, uv=vu=0. Our results generalize the results obtained for bounded linear operators on Hilbert spaces.