Spatial graphoids

To study knotted graphs with open ends arising in proteins, we introduce virtual graphoids, which are virtual spatial graph diagrams with two distinguished degree-one vertices modulo graph Reidemeister moves applied away from the distinguished vertices. Generalizing previously known results, we give topological interpretations of graphoids. By analyzing the Yamada polynomial, we provide bounds for the crossing numbers. As an application, we can produce nontrivial graphoids by verifying that they satisfy adequacy conditions in the same spirit as Lickorish and Thistlethwaite’s notion of adequate links.