Is it OK to use either "mustn't" or "needn't" in such a context?
Writing this report is not important. You[ mustn't _ needn't ] bother yourself.
I know "mustn't" refers to something that is prohibited / negative obligation. However, "needn't" refers to "lack of necessity". Yet, Can't we use "mustn't" for "strong advice" as is mentioned in some sentences.