
theorem Th14:
  for L being non empty ZeroStr, p being Polynomial of L holds p
  is non-zero iff len p > 0
proof
  let L be non empty ZeroStr, p be Polynomial of L;
  hereby
    assume p is non-zero;
    then p <> 0_. L;
    then len p <> 0 by POLYNOM4:5;
    hence len p > 0;
  end;
  assume len p > 0;
  then p <> 0_. L by POLYNOM4:3;
  hence thesis;
end;
