Suppose that C is a smooth plane curve of degree d (d [greater than or equal to] 4).
Referring to [3], we may infer that plane curves with [delta](C) [not equal to] 0 or [delta]'(C) = 0 play an important role when we classify the automorphism group of smooth plane curves.
Let [C.sub.0] be a smooth plane curve with defining equation [F.sub.0](X, Y, Z) = 0.
Let C be a smooth plane curve of degree d [greater than or equal to] 4, G a subgroup of Aut(C).