By assuming that we knew the sentence as "Tony Blair is prime minister or may the moon is made of blue cheese", is true or we later found out that the moon isn't in fact made of cheese. It means that the first disjoined sentence is true; so than we can infer that Tony Blair is indeed prime minister. Hence we say that this typifies the essence of the unit resolution rule:
((A ? B), ¬ B ))/A
So in the generalised version of this inference rule is one subject of a whole area of "Artificial Intelligence" research called as resolution theorem proving, that we cover in detail in the next lecture.