Product kroneckers = new Product();
Indices targetIndices = sp.getIndices();
Indices varIndices = var.getIndices();
for (int i = 0; i < sp.getIndices().size(); ++i)
kroneckers.add(CC.createMetricOrKronecker(targetIndices.get(i), varIndices.get(i)));
return kroneckers.equivalent();
} else if (target.getClass() == TensorField.class) {
TensorField field = (TensorField) target;
Tensor[] args = field.getArgs();
for (int i = 0; i < args.length; ++i)
if (getDerivative(args[i], var) != null)