The ornamental design for a lamp, as shown and described.
FIG. 1 is a perspective view a preferred embodiment of the lamp of my invention;
FIG. 2 is a front elevational view of the lamp;
FIG. 3 is a top plan view of the lamp; and,
FIG. 4 is a side elevational view of the lamp.
A rear elevational view of the lamp is the same as the front elevational view illustrated in FIG. 2. An elevational view from the other side of the lamp is the same as that shown in FIG. 4.