in our manifestly Diff$(M)$ – invariant formulation such techniques never play any role.

After having analyzed the Nambu – Goto string as a constrained dynamical system á la Dirac, in section three we recall the theory of the [**Pohlmeyer Charges**]{}. The string on flat target spaces turns out to be a completely integrable two – dimensional system and the [**Pohlmeyer Charges**]{} are nothing else than the invariants constructed from the corresponding monodromies via Lax pair methods. It is these charges that we want to study interesting representations of.

In section four we recall elements from Algebraic Quantum Field Theory (AQFT). In particular, we describe how cyclic representations of a given $^\ast-$algebra $\mathfrak{A}$ arise via the Gel’fand – Naimark – Segal (GNS) construction once a positive linear functional (a state) $\omega$ is given. This is the same construction that underlies the Wightman reconstruction theorem [@8] (reconstructing a Hilbert space from a set of $n-$point functions subject to the positivity requirement). Moreover, if a symmetry group acts on $\mathfrak{A}$ as a group of automorphisms and if $\omega$ is invariant then the symmetry group can be implemented as a group of unitary operators on the GNS Hilbert space [*without anomalies*]{}.

In section five 