  We investigate the electron tunneling into the edge of a clean weakly
interacting two-dimensional electron gas. It is shown that the corresponding
differential conductance $G(V)$ has a cusp at zero bias, and is characterized
by a universal slope $|dG/dV|$ at $V=0$. This singularity originates from the
electron scattering on the Friedel oscillation caused by the boundary of the
system.
