public EuclideanMatrix4 Curl(LorentzVectorOperatorL del)
 {
     return(new EuclideanMatrix4(MatrixUtilities.MatrixCrossProduct(i => del[i], i => this[i], (x, y) => x - y, (x, y) => x * y)));
 }
 public LorentzMatrixUU Curl(LorentzVectorOperatorU del)
 {
     return(new LorentzMatrixUU(MatrixUtilities.MatrixCrossProduct(i => del[i], i => this[i], (x, y) => x - y, (x, y) => x * y)));
 }