On integrability of systems of evolution equations

We prove the conjecture, formulated in [BSW98], that almost all systems in the family[formula]have at most finitely many symmetries by using number theory. We list the nine exceptional cases when the systems do have infinitively many symmetries. For such systems, we give the recursive operators to generate their symmetries. We treat both 1the commutative and the noncommutative (or quantum) cases. This is the first example of a class of equations where such a classification has been possible. © 2001 Academic Press.