Completeness conjecture for obtuse rational lattice triangles
Completeness conjecture for obtuse rational lattice triangles
Let be a rational triangle, meaning that its angles are rational multiples of . The triangle is a lattice triangle if its unfolding is a translation surface whose -orbit is closed in its stratum. An obtuse triangle has one angle in .
Completeness conjecture. The known list of obtuse rational lattice triangles is complete: every obtuse rational lattice triangle is either a member of one of the two infinite families
and
or is Hooper's triangle with angles
The acute and right-angled cases are described as fully resolved, whereas the classification of obtuse scalene triangles, those with distinct interior angles, remains the primary open challenge.
Progress summary
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Sources & referencesView supporting material
Primary source
David Kurniadi Angdinata, Evan Chen, Ken Ono, Jiaxin Zhang and Jujian Zhang, “On the paucity of lattice triangles”, arXiv:2603.23928 (2026).
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