Envelopes in the class of Banach algebras of polynomial growth and C^∞-functions of a finite number of free variables

We introduce the notion of envelope of a topological algebra (in particular, an arbitrary associative algebra) with respect to a class of Banach algebras. In the case of the class of real Banach algebras of polynomial growth, i.e., admitting a C^∞-functional calculus for every element, we get a functor that maps the algebra of polynomials in k variables to the algebra of C^∞-functions on R^k. The envelope of a general commutative or non-commutative algebra can be treated as an algebra of C^∞-functions on some commutative or non-commutative space. In particular, we describe the envelopes of the universal enveloping algebra of finite-dimensional Lie algebras, the coordinate algebras of the quantum plane and quantum group SL(2) and also look at some commutative examples. A result on algebras of ‘free C^∞-functions’, i.e., the envelopes of free associative algebras of finite rank k, is announced for general k and proved for k⩽2.