  There is an elegant relation found by Fabricius-Bjerre [Math. Scand 40 (1977)
20--24] among the double tangent lines, crossings, inflections points, and
cusps of a singular curve in the plane. We give a new generalization to
singular curves in RP^2. We note that the quantities in the formula are
naturally dual to each other in RP^2, and we give a new dual formula.
