  We propose a reconstruction of the initial system of ordinary differential
equations from a single observed variable. The suggested approach is applied to
a certain class of systems which includes, in particular, the Rossler system
and other chaotic systems. We develop relations and a method to pass from a
model that involves the observable and its time derivatives to a real original
system. To this end, we first find a set of candidates of the system in an
analytic way. After that, by additionally studying the system, we make a choice
for the sought system.
