On irregular links at infinity of algebraic plane curves

We give two proofs of a conjecture of the first author (Inv. Math. 98, 1989) that a reduced algebraic plane curve is regular at infinity if and only if its link at infinity is a regular toral link. This conjecture has also been proved by Ha H.~V. using Lojasiewicz numbers at infinity. Our first proof uses the polar invariant and the second proof uses linear systems of plane curve singularities. The second approach (based on a paper in preparation) also proves a stronger conjecture (loc. cit.) describing topologically the regular link at infinity associated with an irregular link at infinity.