FIG. 1 is a front perspective view of a first embodiment of an ornamental design for a shelf illustrated in a first orientation, with the supporting slot wall shown in dashed lines;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a front perspective view of the shelf of FIG. 1 shown in an optional orientation, which is the reverse of FIG. 1.
The structures depicted by means of broken lines in the figures have been shown for illustrative purpose only and form no part of the claimed design.