Gauss's lemma

Gauss’s lemma Let be an odd prime, be an integer coprime to . Take the least residues of , i.e. reduce them to integers in . Let be the number of members in this set that are greater than . Then

Proof. Q has exactly elements since and is a prime.We can rewrite Q to integers in by rewriting all into .

Corollary Let p be an odd prime. Then

Proof. Because , we only need to find out the cut-off point

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