The ornamental design for a pool, as shown and described.
FIG. 1 is a perspective view of a pool, showing our new design.
FIG. 2 is another perspective view of the pool of FIG. 1.
FIG. 3 is a right side view of the pool of FIG. 1.
FIG. 4 is a left side view of the pool of FIG. 1.
FIG. 5 is a front view of the pool of FIG. 1.
FIG. 6 is a rear view of the pool of FIG. 1.
FIG. 7 is a top view of the pool of FIG. 1; and,
FIG. 8 is a bottom view of the pool of FIG. 1.
The evenly dotted broken lines in the figures illustrate unclaimed features of the pool that form no part of the claimed design. The dash-dot-dash broken lines in the figures define boundary lines that form no part of the claimed design.