  In this paper we consider relations between distributional chaos in a
sequence with distributional chaos, w-chaos, R-T chaos, DC 3, respectively). We
give a sufficient condition and prove that the distributional chaos is
equivalent to the distributional chaos in a sequence under this condition.
Besides, we get that distributional chaos in a sequence and w-chaos(R-T chaos,
DC 3, respectively)do not imply each other. Finally, we give a new definition
of chaos, named DC 2', which is similar to DC 2, and show that for any integer
N > 0, f is DC 2' if and only if f^N is also DC 2'.
