We claim the ornamental design for a sofa, as shown and described.
FIG. 1 is a front perspective view of a sofa according to a first embodiment of the invention.
FIG. 2 is a front perspective view of a sofa according to an alternative embodiment of the invention.
FIG. 3 is a front elevational view of a sofa according to the first embodiment of the invention.
FIG. 4 is a front elevational view of a sofa according to the alternative embodiment of the invention.
FIG. 5 is a top view of a sofa according to the first embodiment of the invention.
FIG. 6 is a top view of a sofa according to the alternative embodiment of the invention; and,
FIG. 7 is a side elevational view of a sofa according to either embodiment of the invention. The view from the opposite side being a mirror image thereof.