reserve X for set;
reserve a,b,c,k,m,n for Nat;
reserve i for Integer;
reserve r for Real;
reserve p for Prime;

theorem Th51:
  3 divides 3|^561-3
  proof
    3|^561-3 = 3*(3|^560-1) by Lm1137;
    hence thesis;
  end;
