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Published online by Cambridge University Press: 31 October 2008
1. A method of characterising plane curves was given by Plücker, who showed that the degree (n), the class (m), and the numbers of nodes (δ), bitangents (τ), cusps (κ), and inflexional tangents (ι) are connected by three independent relations. He showed also that n and m, δ and τ, κ and ι are dual pairs.
1 I am indebted to the referee for these results.