-- | This predicate is true for links which are instantiation morphisms
dglPredInstance :: LEdge DGLinkLab -> Maybe (LEdge DGLinkLab)
dglPredInstance edg@(_, _, DGLink { dgl_origin = DGLinkMorph _ }) = Just edg
dglPredInstance :: LEdge DGLinkLab -> Maybe (LEdge DGLinkLab)
dglPredInstance edg@(_, _, DGLink { dgl_origin = DGLinkMorph _ }) = Just edg
dglPredInstance edg@(_, _, DGLink { dgl_origin = DGLinkMorph _ }) = Just edg