  We propose a definition of a Poincar\'e algebra for a two dimensional
space--time with one discretized dimension. This algebra has the structure of a
Hopf algebra. We use the link between Onsager's uniformization of the Ising
model and the dispersion relation of a free particle in this space--time,
together with the rapidity representation of the quantum deformation of the
Poincar\'e enveloping algebra.
