“…Their rich symmetry structure together with the complicated counterterms needed in their quantum analysis [20], make the problem of their quantization difficult and rather different from the abelian ATFT's [16], [21]. From the other side, due to their integrability, a set of stable nonperturbative classical solutions (solitons and breathers) of these IM's have been recently constructed [15], [16], [17], [22]. This suggests that one can follow further the semiclassical methods [24] of quantization of these solutions in order to derive their nonperturbative particle spectrum, S-matrices, form-factors, etc.…”