/sci/ - Science & Math

I''m stuck with the exercise in pic related. It's about Bayes network.
From the given rules, I can infer that:
X -> (+) Y also means P(y1 | x1, u) > P(y1 | u)
and
X -> (-) Y also means P(y1 | x1, u) < P(y1 | u)

But when it comes down to a reasoning involves 3 nodes (such as D -> C -> T). I don't know how to prove it or where to start.

Thanks in advance.