I've been taught that the word "shall" represent obligatory or mandatory. On the other hand, I was taught by another lecturer that "must" represent mandatory.
Which one of the two represents obligatory. When I asked a teacher this question, he told me "shall" is also synonymous to might or maybe. Is this true?
As an example, consider;
He shall report the case to his senior officer.
He must report the case to his senior officer.