  A reparametrization invariant model, introduced by Montesinos, Rovelli and
Thiemann, possessing an SL(2,R) gauge symmetry is treated along the guidelines
of an algebraic constraint quantization scheme that translates the vanishing of
the constraints into representation conditions for the algebra of observables.
The application of this algebraic scheme to the SL(2,R) model yields an
unambiguous identification of the physical representation of the algebra of
observables.
