The massive phase of two-layer integrable systems is studied by means
of RSOS restrictions of affine Toda theories. A general classification
of all possible integrable perturbations of coupled minimal models is
pursued by an analysis of the (extended) Dynkin diagrams. The models
considered in most detail are coupled minimal models which interpolate
between magnetically coupled Ising models and Heisenberg spin ladders
along the c < 1 discrete series. (C) 1998 Elsevier Science B.V.