Let A be a Ph.D. student who had defined a master project for a master student called B. The topic was indeed a part of the overall Ph.D. problem statement of A. To make it feasibly doable by B, A had already planned the solution strategy, but the detailed composition of a solution and its implementation had to be handled by B. The project was indeed a small open problem whose solution was achieved by extensive participations of A, as well. The project was successfully finished, and B wrote his master thesis including the results. Moreover, a paper was published whose writer and the first author was A. When A starts to write his thesis, may he also bring those results in his own ph.D. thesis? In one hand, those results partially do also belong to him letting him logically claim those contributions. On the other hand, bringing the already-published-in-B-thesis results in his thesis may be an instance of plagiarism.
What's the workaround for A?