Euclid's lemma
In number theory , Euclid's lemma is a lemma that captures a fundamental property of prime numbers , namely: For example , if , , , then , and since this is divisible by 19 , the lemma implies that one or both of 133 or 143 must be as well . 
<triplet> Euclid's lemma <subj> lemma <obj> instance of