Say, A and B are two PhD students working on the same project, and C is their supervisor. D and E are two students working on a similar project to A and B's, and F is D and E's supervisor. The other day C and F met and decided to collaborate. And now the project is about to end, so it's time to write a paper. A, B, D, and E all insist they should be the first author, and no one wants to be the fourth place. In this situation, how should the supervisors decide who's first? And imagine this scenario: B writes the paper without letting anyone know, and then they show this paper to the two groups and ask for the other three people's data. Then does this automatically make B the first author?