  We study the integrable systems in higher dimensions which can be written not
by the Hirota's bilinear form but by the trilinear form. We explicitly discuss
about the Bogoyavlenskii-Schiff(BS) equation in (2 + 1) dimensions. Its
analytical proof of multi soliton solution and a new feature are given. Being
guided by the strong symmetry, we also propose a new equation in (3 + 1)
dimensions.
