The ornamental design for an umbrella, as shown and described.
FIG. 1 is a top, front and right side perspective view of an umbrella, showing my new design;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a rear view thereof; and,
FIG. 7 is a left side view thereof.
The umbrella staff is shown with a symbolic break in length. The appearance of any portion of the article between the break lines forms no part of the claimed design.
Special fold-up umbrella having rib and frame design for easier opening and closing of umbrella, and two canopies designed to stabilize the ribs and vent the air