  Quantum computations are easily represented in the graphical notation known
as the ZX-calculus, a.k.a. the red-green calculus. We demonstrate its use in
reasoning about measurement-based quantum computing, where the graphical syntax
directly captures the structure of the entangled states used to represent
computations, and show that the notion of information flow within the entangled
states gives rise to rewriting strategies for proving the correctness of
quantum programs.
