  In this paper I present overview of two preprints that were published at
Budker Institute of Nuclear Physics in 1980 [1,2]. These original publications
describing harmonic generation technique which has the same foundation as
Echo-Enabled Har-monic Generation (EEHG). They recently become available online
[3], but they are still unknown to FEL community. This paper is an attempt to
cur-rent this omission.
