This is an excellent answer; however, one thing remains unanswered for me. Your last stipulation says,
"He must not be the qualifying child of another taxpayer". Qualifying child? In the circumstances outlined above, you have stated he can be claimed if all the other items are true. He splits his time between his mother (ex-wife) and myself so technically we both qualify to claim him but of course we have an arrangement and only one of us will. Does this make him a qualifying child of more than one taxpayer? And if so, is that the scenario you're describing?
