The ornamental design for a bookcase, as shown and described.
FIG. 1 is a right front perspective view of a bookcase showing my new
design;
FIG. 2 is a left side view thereof, the right side being a mirror image;
and,
FIG. 3 is a partial bottom view thereof.
The top, rear and partial bottom sides are plain and unornamented. The
broken line disclosure is for illustrative purposes only and forms no part
of the claimed design.
Views that are merely plain and/or do not include any ornamentality are not
illustrated in the drawing disclosure.