We've just started studying the decidability notion in our Algorithms class. So far we've only defined it and went through some examples of problems that fit different cases : decidable, semi-decidable, undecidable. But that's it. On our test today, this question popped up:
Consider the predicates $P_1,P_2,Q_1,Q_2 : R$ $\rightarrow \{0,1\}$ such that $P_1 \vee P_2 $ , $Q_1 \vee Q_2 $ are semi-decidable and $P_2 = \overline{Q_2}$. What can be said about $P_1 \vee Q_1 $?
I looked on the web before coming here, but I don't really understand how to approach this kind of problems. Can anyone help?