pure literal

Coursework pure literal is any literal that occurs only positive or negatively in all clauses:

$$(P\vee Q\vee \neg S),(P\vee \neg Q),(Q\vee R),(Q\vee \neg R\vee \neg S)$$

We can always add these literals to our assignment without a risk of conflict:

$$P:=\top ,S:=\perp$$

Hence we can eliminate any clause containing these pure literals:

$$\cancel{(P\vee Q\vee \neg S)},\cancel{(P\vee \neg Q)},(Q\vee R),\cancel{(Q\vee \neg R\vee \neg S)}$$