We claim the ornamental design for a lamp, as shown and described.
FIG. 1 is a perspective view showing an embodiment of our design for a lamp.
FIG. 2 is a side view of the embodiment of our design shown in FIG. 1. Since all sides of the lamp appear the same, save for broken line portions, which are directed to environmental features, this is the only side view shown.
FIG. 3 is a top view of the embodiment of our design shown in FIG. 1; and,
FIG. 4 is a bottom view of the embodiment of our design as shown in FIG. 1.
The broken line showing of the lower portions of the lamp is included for the purpose of illustrating only and forms no part of the claimed design.