  In this note we show how a initial value problem for a relaxation process
governed by a differential equation of non-integer order with a constant
coefficient may be equivalent to that of a differential equation of the first
order with a varying coefficient. This equivalence is shown for the simple
fractional relaxation equation that points out the relevance of the
Mittag-Leffler function in fractional calculus. This simple argument may lead
to the equivalence of more general processes governed by evolution equations of
fractional order with constant coefficients to processes governed by
differential equations of integer order but with varying coefficients. Our main
motivation is to solicit the researchers to extend this approach to other areas
of applied science in order to have a more deep knowledge of certain phenomena,
both deterministic and stochastic ones, nowadays investigated with the
techniques of the fractional calculus.
