The ornamental design for a lamp, as shown and described.
FIG. 1 is a perspective view of a lamp showing my new design, the lamp
being lit so that the light source produces multiple reflections on the
side and top one-way mirror panels;
FIG. 2 is a typical side elevational view thereof, the lamp being unlit;
FIG. 3 is a top plan view thereof, the lamp being unlit; and