Resolution Proofs Im doing a past paper and this question came up, I've only seen Resolution proofs online and in the past with an OR symbol between two letters but this question is different. It asks me too pick the proofs that hold. Could someone offer some help and explanations, the answer is not needed as they are given.


See Resolution; the symbol : 

$\{ x,y \}$

stay for a (disjunctive) clause, that is a disjunction of literals :
$x \lor y$.
Thus, for example, the proof in i. amounts to :
1) $x \lor y$ --- premise
2) $x \lor \lnot y$ --- premise
3) $x$ --- from 1) and 2) by resolution rule
4) $\lnot x$ --- premise

5) $\square$ (the empty clause) --- from 3) and 4).

