What is claimed is the ornamental design for a lamp, as shown.
FIG. 1 is a top perspective view of the lamp positioned in a first position;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof;
FIG. 8 is a perspective view of the lamp positioned in a second position; and,
FIG. 9 is a perspective view of the lamp positioned in a third position.
The portions of the lamp shown in broken lines form no part of the claimed design. The lamp is shown with symbolic breaks in its length. The appearance of any portion of the article between the break lines form no part of the claimed design.