  This is an old article which has never been posted for public use and which
only appeard in a relatively hard-to-get Proceedings of the Sakharov Conference
in Moscow (May, 1991). The subject of this article has received a lot of
attention in last two years. Although we acknowledge that there has been a very
big progress in the field of relating the spectrum of fluctuations to scalar
field potentials of inflation models, which have outdated some of our results
(particularly because we never took into account the tensor fluctuations which
have been shown to be crucial for reconstructing the inflaton potential) we
think that some of the other ideas and approaches which we presented in this
article maybe still of interest. We did not rewrite the article to include any
of the newer approaches and we did not add any of the newer references. The
reader is advised to refer to recent papers (for example, see the paper
astro-ph/9403001 by Edward Kolb and Sharon Vadas) for state of the art review
and up-to-date references.
  ==The original abstract of the article==: We prove that, in stochastic
approach, there exists an equivalence relation between different inflationary
models under some redefinition of field and time variables. The
postinflationary physics is insensitive to it and one can say that related
theories are in fact indistinguishable from the viewpoint
