“…The technics rely on basic harmonic and functional analysis, and we tried to keep a reasonnable balance between self-containedness and heaviness of the calculus : when proofs are slight modifications of already existing arguments we often point to a reference instead of repeating them, and if several quantities are bounded by the same method the precise argument is detailed only once. Our main result is that there exists N ∈ N and an interpolation operator Π : l 2 (N hZ) → l 2 (hZ) actually constructed for N = 6 such that the semi-discrete finite difference problem ∂ t u n + ∂ 3 h u n + (∂ h ΠEu) 5 n /5 = 0, (n, t) ∈ Z × R, u| t=0 = Πu 0,h , is globally well-posed for u 0,h ∈ l 2 (N hZ) sufficiently small, and the solution satisfies dispersive estimates analogous to (D1, D2) uniformly in h. The notations E, Π, ∂ h and ∂ 3 h are defined in the first and second sections. The convergence of the discrete solution is proved by standard weak convergence/compactness arguments.…”