Differential Geometry of Plane Curves — Selected Topics

April 2026  ·  IMT, Toulouse, France
Professor Gil Bor, CIMAT, Guanajuato, Mexico (visiting IMT) - gil@cimat.mx
Directed to Master students M1 and M2, mainly (but all interested public, students and faculty, are welcome).
Schedule & room 4 sessions total, can be extended upon demand.
  • 15/0410h – 12h  (U4-202)
  • 16/0413h30 – 15h30  (U4-202)
  • 21/0410h – 12h  (U4-211)
  • 22/0410h – 12h  (U4-211)

Description. This is a topics course covering classical aspects of the differential geometry of plane curves, as well as some contemporary variations and developments (as time permits). The emphasis is less on definitions and more on interesting examples and nice results: the 4-vertex theorem, the Tait–Kneser nesting theorem, evolutes and involutes, bicycle trajectories, the classical curves (cycloid, catenary, tractrix, elasticae, …). The prerequisites are a standard undergraduate vector calculus course, curiosity, and a mind open to new ideas.


Sessions:
1: The osculating circle, the Tait-Knesser Theorem --> Notes
2: Envelopes of curves, The 4 vertex theorem --> Notes
3: The tractrix, bicycle mathematics --> Notes
4: The geometry of Kepler orbits --> Article


The figure illustrates the Tait–Kneser theorem, on the nesting of the osculating circles along a plane curve with monotone curvature (in this case an Archimedean spiral). Taken from the article Variations on the Tait–Kneser Theorem (with C. Jackman and S. Tabachnikov), Math. Intelligencer 43 (2021).
Tait–Kneser theorem illustration

(click to enlarge)