reserve n,k,b for Nat, i for Integer;

theorem Th22:
  7,10 are_coprime
  proof
    2,7 are_coprime & 5,7 are_coprime by NAT_4:26,EULER_1:2;
    then 2*5,7 are_coprime by INT_2:26;
    hence thesis;
  end;
