In a now deleted comment of this question, the OP said it is a homework from a friend. Then I edited the question to add homework tag, and the edit was rejected. I think this is my own fault for not giving enough explanations in the edit.
As this is not the first time my edit is rejected, I wonder whether there is a way to have some sort of communication with the people who reject. I could re-iterate my edit adding more explanations, but I do not really like to do so, it is a little like an edit war.