2006/10/17 by A. Yu. Pirkovskii, Pirkovskii, A. Yu.
Mathematics · #16D40 #18G50 #46H25 #46M10 #FOS: Mathematics #Functional Analysis (math.FA) #Primary 46M18 #Secondary 46A45 #math.FA #msc:16D40 #msc:18G50 #msc:46A45 #msc:46H25 #msc:46M10 #msc:46M18
paper · pdf · doi:10.48550/arxiv.math/0610528
32 pages
arxiv created 2006/10/17 · arxiv updated 2009/12/01
Let A be a locally m-convex Fréchet algebra. We give a necessary and sufficient condition for a cyclic Fréchet A-module X=A+/I to be strictly flat, generalizing thereby a criterion of Helemskii and Sheinberg. To this end, we introduce a notion of "locally bounded approximate identity" (a locally b.a.i. for short), and we show that X is strictly flat if and only if the ideal I has a right locally b.a.i. Next we apply this result to amenable algebras and show that a locally m-convex Fréchet algebra A is amenable if and only if A is isomorphic to a reduced inverse limit of amenable Banach algebras. We also extend a number of characterizations of amenability obtained by Johnson and by Helemskii and Sheinberg to the setting of locally m-convex Fréchet algebras. As a corollary, we show that Connes and Haagerup's theorem on amenable C^*-algebras and Sheinberg's theorem on amenable uniform algebras hold in the Fréchet algebra case. We also show that a quasinormable locally m-convex Fréchet algebra has a locally b.a.i. if and only if it has a b.a.i. On the other hand, we give an example of a commutative, locally m-convex Fréchet-Montel algebra which has a locally b.a.i., but does not have a b.a.i. Some of the results of this paper were announced in ArXiv preprint math.FA/0511132.