The ornamental design for a fan, as shown and described.
FIG. 1 is a front isometric view showing the new design.
FIG. 2 is a rear isometric view thereof.
FIG. 3 is a front view thereof.
FIG. 4 is a right side elevation view thereof.
FIG. 5 is a left side elevation view thereof.
FIG. 6 is a top plan view thereof.
FIG. 7 is a bottom plan view thereof.
FIG. 8 is an enlarged partial view of FIG. 1.
FIG. 9 is an enlarged partial view of FIG. 2; and,
FIG. 10 is an enlarged partial view of FIG. 3.
The dashed lines shown in the drawings illustrate portions of the fan that are not claimed and thus form no part of the claimed design. The shading lines shown in the drawings represent the three- dimensional contour of the claimed design and are not intended to indicate surface decoration.