“…Here the role of A in (1) is played by the family of matrices A(z) = A -zD, where z _> 0. The main difference between problem and (1), (3), and (4) is the fact that if there exists z 0 >_ 0 such that A(z o) has an eigenvalue with a zero real part (and no positive part), then infinitely many characteristic exponents of the linear problem, which correspond to (5) and (4) with F = 0, will tend to zero as e, /z -~ 0. Consequently, the dimension of the critical case must be considered as infinite.…”