The ornamental design for a stool, as shown and described.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
1.1is a perspective view of a stool, showing my new design;
1.2is a left view thereof;
1.3is a right view thereof;
1.4is a front view thereof;
1.5is a rear view thereof;
1.6is a top view thereof; and
1.7is a bottom view thereof.
In reproduction 1.7, the areas colored in red show protions of the article that form no part of the claimed design. The broken lines show portions of the article that form no part of the claimed design.