If an algebraic surface F of order J > ^ 4 has a double line (either nodal or cuspidal), the anomaly A of the plane sections C of a tangent cone to F is A = (1/6) v(v — 4) (v — 5). As is evident from this expression for A, plane curve systems C associated with a surface having a double line are anomalous only for v^6. When z> = 3, the above formula yields A = l. However, a cubic surface with a ...
