“…for u = u(t, x) : R × T → N, where (N, J, h) is a compact Kähler manifold, and b 1 = 0, b 2 , b 3 , b 4 ∈ R are real constants. As in [19], the equation (1.3) is actually generalized also as (1.4) where N = S 2 , b 1 = a 1 , b 2 = 1, b 3 = a 2 − a 1 , and b 4 = −5a 1 + 2a 2 . In fact, (1.1) and (1.4) are essentially the same, if (N, J, h) is a Riemann surface with constant Gaussian curvature.…”