The ornamental design for a lamp, as shown and described.
FIG. 1 is a front elevational view of a lamp showing my new design, the rear and side elevational views being identical in appearance;
FIG. 2 is a top plan view thereof, the bottom plan view being identical in appearance;
FIG. 3 is a front elevational view thereof, with the shade portions removed, the broken line disclosure representing portions of the lamp which form no part of the claimed design, and the rear elevational view being identical in appearance; and,
FIG. 4 is a top plan view thereof; with the shade portions removed, the broken line disclosure representing portions of the lamp which form no part of the claimed design, and the bottom plan view being identical in appearance.
The dashed broken lines shown in the drawings illustrate environmental features that form no part of the claimed design.