theorem
  for n be non zero Element of NAT, z be Complex for v be CRoot
  of n,z st v = 0 holds z = 0
proof
  let n be non zero Element of NAT, z be Complex;
  let v be CRoot of n,z;
  assume v = 0;
  then 0|^ n = z by COMPTRIG:def 2;
  hence thesis by Lm2;
end;
