ELA, Volume 15, pp. 154-158, May 2006, abstract.

On Polynomials in Two Projections

Ilya M. Spitkovsky

Conditions are established on a polynomial f in two 
variables under which the equality f(P_1,P_2)=0 for 
two orthogonal projections P_1, P_2 is possible only 
if P_1 and P_2 commute.