Today this question was put on Hold as off-topic

https://mathoverflow.net/questions/186117/solutions-for-categories-for-the-working-mathematician

I wander if this is a disservice in fact. I suspect that a graduate student might benefit from such solutions while learning and this is part of research. Is not as if he's asking for solutions to Calculus homework. I'm not particularly inclined to suggest to reopen the question, just that I am not sure if we would actually be more helpful if we would leave these kinds of questions open.