  We build on our construction of Hopf algebroids from noncommutative calculi
under the further assumption of surjectivity for the calculus. We also
introduce the notions of Hopf ideals and isotopy quotients for arbitrary Hopf
algebroids. Using these ingredients, we prove a Riemann-Hilbert correspondence
for digraphs, by showing that the groupoid algebra of the fundamental groupoid
of a digraph is isomorphic to the isotopy quotient of the Hopf algberoid
corresponding to flat connections over the digraph.
