All Y-friezes come from SL2-friezes
Abstract
We resolve a conjecture of de Saint Germain: all Y-friezes arise from SL2-friezes. Additionally, we give a threefold characterisation of those SL2-friezes that give rise to the same Y-frieze: an elementary characterisation using quiddities, a combinatorial characterisation using triangulated polygons, and a geometrical characterisation using chains of horocycles.
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