For γt: S1→C, a smooth
homotopy of closed curves, the changing configuration of vertices and cusps is studied
by considering the set in I ×S1×S1 given by (γt(z) −γt(ζ))∕(z −ζ) = 0. The main
tool is oriented intersection theory from differential topology. The results relate to
previous work by Whitney and Titus on normal curves and intersection
sequences.