Isotropy quotients of Hopf algebroids and the fundamental groupoid of digraphs (Q2675080)

Based on author's abstract: The author extends his construction of Hopf algebroids from non-commutative calculi under the further assumption of surjectivity for the calculus. Moreover, the author introduces the notions of Hopf ideals and isotropy quotients for arbitrary Hopf algebroids. Then the Riemann-Hilbert correspondence for digraphs is shown. Namely, the author shows that the groupoid algebra of the fundamental groupoid of a digraph is isomorphic to the isotropy quotient of the Hopf algebroid corresponding to flat connections over the digraph.