The ornamental design for a lamp, as shown and described.
FIG. 1 is a perspective view of a lamp showing my new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a right side elevational view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof;
FIG. 9 is an exploded perspective view of the lamp; and,
FIG. 10 is an enlarged view of portion 10 shown in FIG. 1.
The lamp is shown with symbolic breaks in its length and the appearance of any portion of the lamp between the break lines form no part of the claimed design. The dot-dash broken lines represent boundaries of the enlarged portion and form no part of the claimed design.