theorem
  for z1,z2 st cpx2euc(z1)=cpx2euc(z2) holds z1=z2
proof
  let z1,z2;
  assume
A1: cpx2euc(z1)=cpx2euc(z2);
  z2 = euc2cpx(cpx2euc(z2)) by Th1;
  hence thesis by A1,Th1;
end;
