code: private void boundaryAreaExteriorLine_(int half_edge, int id_a, int id_b) {
  		if (m_matrix[MatrixPredicate.BoundaryExterior] == 1)
  			return;
  
  		int parentage = m_topo_graph.getHalfEdgeParentage(half_edge);
  
  		if ((parentage & id_a) != 0 && (parentage & id_b) == 0)
  			m_matrix[MatrixPredicate.BoundaryExterior] = 1;
  
  	}
docs: with the exterior of Line B.