Abstract. A locally C * -algebra is contractible iff it is topologically isomorphic to the topological cartesian product of a certain family of full matrix algebras.
IntroductionAt the beginning of the 1970's a well-known series of papers by J. L. Taylor appeared, viewing his concepts of joint spectrum and multi-operator functional calculus under the light of homology. By the requirements of his theory [13], J. L. Taylor developed in [12] important homological methods in the general framework of topological algebras. In the latter paper, among other interesting results, Proposition 5.7 was presented, which loosely speaking, has the following meaning: A contractible Arens-Michael algebra is topologically isomorphic to the direct sum of the topological cartesian product of a certain family of full matrix algebras and of some hypothetical "badly behaving" algebra, which in the commutative case is always zero. Around the 1980's A. Ya. Helemskii traced back a gap in the proof of the preceding result, which was filled by himself in 1985 in the case where the algebra under consideration is moreover commutative; for a proof of this result, see [5, Theorem IV. 5.27]. The aforementioned Taylor's result initiates a more general problem of whether an arbitrary contractible Arens-Michael algebra is topologically isomorphic to the topological cartesian product of a certain family of full matrix algebras. This, among other questions, was considered by the school of Helemskii in Moscow, with successful answers in several cases. Nevertheless, the main problem still remains open, even in the normed case (see [5, p. 195, comments after Exercise 5.28]). More precisely, in 1996, positive answers were given by Y. V. Selivanov [11] for contractible semiprime Fréchet Arens-Michael algebras having a nice geometrical property, the so-called "approximation property" of A. Grothendieck (cf. e.g.,