New hidden symmetries in 2-dimensional models

In an attempt to derive the hidden symmetries for some integrable 2-dimensional models by considering the invariances of the corresponding linearization systems and the Riemann-Hilbert transformations, we arrive at a new ''sub''-algebra of the ordinary Kac-Moody algebra which represents the hidden symmetry for for example the sine-Gordon theory. A similar ''sub''-algebra is found for the Liouville model. These new algebras differ from the ordinary ones in having a different structure according to whether the grading is even or odd. We describe a new systematic way of finding such hidden symmetries from general linearization systems. (orig.)