> g = NamedMorphism(B, C, "g")
        >>> diagram = Diagram([f, g])
        >>> grid = DiagramGrid(diagram)
        >>> grid.morphisms
        {NamedMorphism(Object("A"), Object("B"), "f"): EmptySet,
        NamedMorphism(Object("B"), Object("C"), "g"): EmptySet}

        N)