public static Transformation createSubstitution(Tensor from, Tensor to) {
if (TensorNumber.isZero(to)) {
if (!(from instanceof SimpleTensor))
throw new UnsupportedOperationException();
return new ZeroSimpleTensorSubstitution((SimpleTensor) from, CC.withMetric());
}
return createSubstitution(from, to, CC.withMetric());
}