Jordan form of the difference of projectors

The Jordan canonical form of the difference of projectors $P-Q$ for the eigenvalues $\lambda\ne- 1, 0, 1$ is proved to be made up of pairs of Jordan blocks; i.e., if there are several blocks $J_k(\lambda)$, then there are exactly the same number of blocks $J_k(-\lambda)$. For a block $J_k(\pm1)$ with $k>1$, there is necessarily a pair block $J_l(\mp1)$, where $|k-l|<1$.