Billiard Trajectories in Regular Polygons and Geodesics on Regular Polyhedra Dmitry Fuchs Problem Contribution 07 January 2021 Pages: 493 - 517
Strange Duality Between the Quadrangle Complete Intersection Singularities Wolfgang EbelingAtsushi Takahashi Research Contribution Open access 22 June 2021 Pages: 519 - 540
Real Lines on Random Cubic Surfaces Rida Ait El ManssourMara BelottiChiara Meroni Research Contribution Open access 02 July 2021 Pages: 541 - 559
On a Theorem of Lyapunov–Poincaré in Higher Dimensions V. LeónB. Scárdua Research Contribution 13 July 2021 Pages: 561 - 571
Surfaces of Section for Seifert Fibrations Bernhard AlbachHansjörg Geiges Research Contribution Open access 05 August 2021 Pages: 573 - 597
Element-Building Games on \(\mathbb {Z}_n\) Bret BeneshRobert Campbell Research Contribution 18 August 2021 Pages: 599 - 608
An Extension of the \(\mathfrak {sl}_2\) Weight System to Graphs with \(n \le 8\) Vertices Evgeny Krasilnikov Research Contribution 06 September 2021 Pages: 609 - 618
New Invariants of Poncelet–Jacobi Bicentric Polygons Pedro RoitmanRonaldo GarciaDan Reznik Research Contribution 18 August 2021 Pages: 619 - 637