Integrating infinite-dimensional Lie algebras by a Tannaka   reconstruction (Part I)
  Let g be a Lie algebra over a field F of characteristic zero, let C be a certain tensor category of representations of g, and C-du a certain category of duals. By a Tannaka reconstruction we associate to C and C-du a monoid M with coordinate ring of matrix coefficients F[M], (which has in general no natural coalgebra structure), as well as a Lie algebra Lie(M). We interprete the monoid M algebraic geometrically as a weak algebraic monoid with Lie algebra Lie(M). The monoid M acts by morphisms of varieties on every object of C, the Lie algebra Lie(M) acts by the differentiated action.   If g is in a natural way a subalgebra of Lie(M), we say that C and C-du are good for integrating g. In this situation we treat: The adjoint action of the unit group of M on Lie(M). The relation between g and M-invariant subspaces. The embedding of F[M] in the dual of the universal enveloping algebra of g. A Peter-and-Weyl-type theorem if the category C is semisimple. The Jordan-Chevalley decompositions for certain elements of M and Lie(M). An embedding theorem related to subalgebras of g which act locally finite. Prounipotent subgroups of M, and generalized toric submonoids of M. We show that C and C-du are good for integrating g, if the Lie algebra g is generated by integrable locally finite elements. 
Claus Mokler