ABSTRACT
In the quantum theory we have to keep track of the factors. Compared to the Feynman rules, the propagator will come with an extra factor. The same factor applies for using the tree-level diagrams to solve the classical equations of motion. It is easy to see that these Feynman rules give identical results for these tree-level diagrams, as compared to the Feynman rules. Due to the multiple commutators, all components that do not commute are connected. However, if the components would commute they would not contribute to the commutators. The combinatorial factors are clearly independent of the space-time integrations and possible contractions of vector or other indices.
