Segre’s lemma of tangents dates back to the 1950’s when he used it in the proof of his “arc is a conic” theorem. Since then it has been used as a tool to prove results about various objects including internal nuclei, Kakeya sets, sets with few odd secants and further results on arcs. Here, we survey some of these results and report on how re-formulations of Segre’s lemma of tangents are leading to new results.
Ball, S., Csajbók, B. On Segre's lemma of tangents. "Electronic notes in discrete mathematics", 1 Juliol 2018, vol. 68, p. 11-16.