On the Propagation of Regularity of Solutions to the KdV Equation on the positive Half-line

We study special regularity properties of solutions to the initial-boundary value problem associated with the Korteweg-de Vries equations posed on the positive half-line. In particular, for initial data $u_0\in H^{{\frac{3}{4}}^{+}}({\mathbb{R}}^{+})$ and boundary data $f\in H^{{\frac{3}{2}}^{+}}({\mathbb{R}}^{+})$, where the restriction of $u_0$ to some subset of $(b,\mathrm{\infty })$ has an extra regularity for any $b>0$, we prove that the regularity of solutions $u$ moves with infinite speed to its left as time evolves until a certain time $T^{\ast }$. The existence of a stopping time $T^{\ast }$ appears because of the effect of the boundary function $f$. Also, as a consequence of our proof, we prove a gain in the regularity of the trace derivatives of the solutions for the Korteweg-de Vries on the half-line.