The ornamental design for a sofa, as shown and described.
FIG. 1 is a front perspective view of a sofa showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a side view thereof;
FIG. 4 is a back view thereof;
FIG. 5 is a back left perspective view thereof; and,
FIG. 6 is a front perspective view in a representative position of a sofa with the broken lines illustrating optional stitching elements not claimed thereof.
The broken lines depicting additional furniture portions (including, for example, pillows, nail heads and stitching) in FIGS. 1–6 represent environmental elements only and form no part of the claimed design. The views of the sofa not shown form no part of the claimed design.