IDEMPOTENTS IN GROUP RINGS By
نویسندگان
چکیده
It is then easily verified that RG satisfies the ring axioms; in fact, RG is a linear algebra over R. (We write all groups multiplicatively, and denote group identities by 1; we also use 1 for the unit element of R if there is one.) If R, in addition to being a ring, is a Banach algebra (i.e., an algebra over the complex field K, with a submultiplicative norm which makes R a Banach space), then we can consider the larger ring Rl(G) which consists of those R-valued functions f on G, with possibly infinite support, for which the norm
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