Pythagorean theorem

a project to generalize the notion of essential codimension due to Brown–Douglas–Fillmore, as well as to understand its ramifications.

Kadison's Pythagorean theorem (2002) provides a characterization of the diagonals of projections with a subtle integrality condition. Arveson (2007), Kaftal, Ng, Zhang (2009), and Argerami (2015) all provide different proofs of that integrality …