Soliton solutions of a coupled modified KdV equations

The multisoliton solution to a system of nonlinear partial differential equations which is expressed by partial derivative vi/partial derivative t + 6 (Sigma(1 less than or equal to j < k less than or equal to N)c(jk)v(j)v(k)) partial derivative vi/partial derivative x + partial derivative 3vi/partial derivative x3 = 0, for i = 1, 2, ..., N where the coefficients c(jk) are arbitrary constants, is expressed by the pfaffians.