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I am reading "An elementary proof of a fundamental theorem in the theory of Banach algebras" by C.E.Rickart, available for instance on https://projecteuclid.org/euclid.mmj/1028998012

The concepts of "circle operation", quasi-regularity and quasi-inverses are new to me, so I am trying to understand every individual formula in detail.

enter image description here

It is interesting how Rickart is using here formally an identity element, although this might be actually not existing. Now when I did the calculation following "An application of this relation, along ... gives" myself, I got $(1-x^0)h(1-x^0)=hk-x^0hk-k$

Please mark the term $-x^0hk$ in my right-hand side instead of $+x^0hk$ in the screenshot. Is this observation correct, i.e. is the "+" in the screenshot a typo?

The rest of the proof of continuity of quasi-inversion goes through without change and is clear to me.

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