“…Readers may refer to R. Temam's book [15] for Galerkin's decomposition and corresponding wellposedness framework applied to dissipative equations. Besides, KdV (Korteweg-de Vries) equations are proved to possess periodic solutions by one of the authors, if similar assumption that the force has small amplitude holds (see, e.g., [16,17,20]). Instead of Galerkin's method as solution of KdV equation doesn't have form of Galerkin-type decomposition, the proof is mainly based on one of local wellposedness results in a particular Sobolev space Y t,T (defined on time interval [t, t + θ] with a particular T including smoothing effects; see next section) in J.…”