Remarks on duality in graph spaces of first-order linear operators

Graph spaces provide a setting alternative to Sobolev spaces and BV spaces, which is suitable for the analysis of ?rst-order linear boundary value problems such as Friedrichs systems. Besides investigations of the well-posedness of the continuous problem there is also an increasing interest in the error analysis of ?nite element methods within a graph space framework. In this text we elucidate various methods for an explicit representation of dual spaces of graph spaces.