  We argue that complex systems, defined as non-Poisson renewal process, with
complexity index $\mu$, exchange information through complexity matching. We
illustrate this property with detailed theoretical and numerical calculations
describing a system with complexity index $\mu_{S}$ perturbed by a signal with
complexity index $\mu_{P}$. We focus our attention on the case $1.5 \leq \mu_S
\leq 2$ and $1 \leq \mu_{P} \leq 2$. We show that for $\mu_{S} \geq \mu_P$, the
system S reproduces the perturbation, and the response intensity increases with
increasing $\mu_P$. The maximum intensity is realized by the matching condition
$\mu_P = \mu_S$. For $\mu_{P} > \mu_{S}$ the response intensity dies out as
$1/t^{\mu_P-\mu_S}$.
