The ornamental design for a stool, as shown and described.
FIG. 1 is a perspective view from the front and side of stool in the form
of an ottoman or footstool, showing my new design (the rear and opposite
side views being mirror images of the front and side shown).
FIG. 2 is a side elevational view thereof.
FIG. 3 is a view in top plan of the stool of FIG. 1.