How to avoid authorship drama in this situation? There are so many posts regarding authorship disputes on this site.  How can my friend, A, avoid such a drama in the following situation?


A and another graduate student, B, are in the same PhD program in the US.
Even though B has just started the program, he completed a MSc program in Europe with research experiences, and he has a de-facto advisor C, who also supervises A.
A while ago, C wrote to A suggesting that A work on a project P, adding that B would work on another project Q.  P and Q are of the same nature but on different objects.  Q builds on B's MSc thesis.
A wished that C assigned him Q instead because Q was about the same object about which A's other project R was.  After working on P, A found that P has a rather trivial answer.
A realized that Q, if solved, gives some progress on R.  Upon telling this to C, A gets a recommendation from C that A talk about Q with B.
After being told about the idea, B told A that he had not completed Q and that he was happy to talk about Q with A.
A realized that his previous idea about the relationship between Q and R was wrong, but instead he came up with an another idea, which would solve Q.  A sent C an email explaining this idea.
While waiting an answer from C, A gets bored and wants to work on his idea.  


Obviously, A does not want to be in the center of an authorship disputes.  How should he proceed?
The explanation is quite convoluted but this looks like a rather common situation: A and B work on closely related topics, both supervised by C. 

First an observation:


  While waiting an answer from C, A gets bored and wants to work on his idea. 


If the waiting is a couple of days that's completely fine to start exploring the idea. But if it's more like a couple of months there's a communication problem that needs to be solved. 

As long as there's no conflict between these three persons, there's no reason why this should lead to authorship dispute. The key is to maintain clear and regular communication, and apparently the three persons involved are aware of that. A is right to seek their supervisor's advice, ultimately the supervisor decides who works on what. But in general there's absolutely no problem for A and B to work on the same idea and write papers together, as long as roles are clearly defined beforehand. In particular the question of who is first author for a particular paper should be clarified from the start. If relevant, the authors could target two distinct papers, one focusing on A's part and the other on B's part.

Note: this might depend on the domain, but I think most academics would agree that an idea by itself doesn't belong to anybody. What matters is the effort put into developing the idea into a proper scientific contribution, usually in the form of a paper: that's authorship. Of course, the person who had the idea should normally be the one developing it, but it's more a matter of common courtesy than of intellectual property.