  I relate contextuality to line bundles. Line bundles are important in
algebraic geometry, they determine through their global sections rational maps
to projective spaces. I explain how such maps, if they exist, relate rationally
the input and output of measurement based computation (MBQC) and show
geometrically that, indeed, contextuality is a necessary resource for the
computational advantage in MBQC. I also leverage the definition of MBQC to
category theory and present it as a "subfunctor" of the spectral presheaf. In
general, the MBQC functor is pointless whereas the computation is trivial.
