reserve X for set;
reserve a,b,c,k,m,n for Nat;
reserve i,j for Integer;
reserve r for Real;
reserve p,p1,p2 for Prime;

theorem Th12:
  n divides 10 implies n = 1 or n = 2 or n = 5 or n = 10
  proof
    10 = 2*5;
    hence thesis by Lem2,XPRIMES1:2,5;
  end;
