Approximation by invertibles

Gartenberg, Michael

doi:10.1090/S0002-9939-1976-0435858-X

Approximation by invertibles
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by Michael Gartenberg

Proc. Amer. Math. Soc. 61 (1976), 341-346

DOI: https://doi.org/10.1090/S0002-9939-1976-0435858-X

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Abstract:

The uniform closure of the set of invertibles of certain ${C^{\ast }}$-algebras is characterized. It is shown that indices on $\mathcal {G}(C(A))$, where $A$ is a closed annulus in the plane and on $M_2^{{S^2} \times {S^1}}$ have continuous extensions to elements which are not invertible.

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