“…Soon, Zakharov (1966) rederived KE (1) using the technique of the Hamiltonian formalism (see also, Zakharov et al 1992;Badulin et al, 2005). Since late 60s, the KE became a separate subject of studying (e.g., Zakharov and 20 Filonenko, 1966;Zakharov and Zaslavskii, 1982;Webb, 1978;Masuda, 1980;Hasselmann and Hasselmann, 1981;Hasselmann et al, 1985;Polnikov, 1989Polnikov, , 1990Polnikov, , 1996Polnikov, , 2007Resio and Perrie, 1991;Pushkarev et al, 2003;Badulin et al, 2005;Young and Van Vledder, 2003;Van Vledder, 2006;Badulin and Zakharov (2017); Geodjaev and Zakharov 2017;Zakhariov, 2017, and references therein). Among them, analytical results found by Zakharov and co-authors (see below) play the crucial role in these investigations.…”