Combinatorial groupoids, cubical complexes, and the Lovasz conjecture

A foundation is laid for a theory of combinatorial groupoids, allowing us to use concepts like holonomy'', parallel transport’‘, bundles'', combinatorial curvature’’ etc. in the context of simplicial (polyhedral) complexes, posets, graphs, polytopes and other combinatorial objects. A new, holonomy-type invariant for cubical complexes is introduced, leading to a combinatorial ``Theorema Egregium’’ for cubical complexes non-embeddable into cubical lattices. Parallel transport of Hom-complexes and maps is used as a tool for extending Babson-Kozlov-Lovasz graph coloring results to more general statements about non-degenerate maps (colorings) of simplicial complexes and graphs.