These posts summarize and review classics of mathematical research. 

Ptolemy Relations and Friends

AUTHOR: A. Felikson (Updated 4/4/23): In recent decades, identities similar to the one in Ptolemy’s theorem started to pop up in many fields in connection to the notion of cluster algebras introduced and studied since 2000 by Fomin and Zelevinsky. In this brief note we will try to describe several animals from this big and rich zoo.

Read More »