ABSTRACT
The most convenient of all conditions in Lemma 6.1 to verify is (6.3)i this condition is usually fulfilled in many applications. The most interesting condition, however, is (6.6). First of all, this condition is fulfilled if the evolution operator is defined by formula (1.19), and thus in this case the statement of Lemma 6.1 holds true. Moreover, (6.6) is always satisfied in the case of a finite system which is obtained in the usual way from the higher order equation
with commuting coefficients, Le.
