private static EdgeAggregator ConstructExteriorRelationship(Triangle tri, Angle extAngle)
        {
            //
            // Acquire the remote angles
            //
            Angle remote1 = null;
            Angle remote2 = null;

            tri.AcquireRemoteAngles(extAngle.GetVertex(), out remote1, out remote2);

            //
            // Construct the new equation
            //
            Addition sum = new Addition(remote1, remote2);
            GeometricAngleEquation eq = new GeometricAngleEquation(extAngle, sum);

            //
            // For the hypergraph
            //
            List <GroundedClause> antecedent = Utilities.MakeList <GroundedClause>(tri);

            antecedent.Add(extAngle);

            return(new EdgeAggregator(antecedent, eq, annotation));
        }