  Physically natural assumption says that the any relaxation process taking
place in the time interval $[t_{0},t_{2}]$, $t_{2} > t_{0}\ge 0$ may be
represented as a composition of processes taking place during time intervals
$[t_{0}, t_{1}]$ and $[t_{1},t_{2}]$ where $t_{1}$ is an arbitrary instant of
time such that $t_{0} \leq t_{1} \leq t_{2}$. For the Debye relaxation such a
composition is realized by usual multiplication which claim is not valid any
longer for more advanced models of relaxation processes. We investigate the
composition law required to be satisfied by the Cole-Cole relaxation and find
its explicit form given by an integro-differential relation playing the role of
the time evolution equation. The latter leads to differential equations
involving fractional derivatives, either of the Caputo or the Riemann-Liouville
senses, which are equivalent to the special case of the fractional
Fokker-Planck equation satisfied by the Mittag-Leffler function known to
describe the Cole-Cole relaxation in the time domain.
