reserve z,z1,z2 for Complex;
reserve r,x1,x2 for Real;
reserve p0,p,p1,p2,p3,q for Point of TOP-REAL 2;

theorem Th13:
  euc2cpx(-p)= -euc2cpx(p)
proof
  -euc2cpx(p) = -(p`1)+(-(p`2))*<i>;
  hence thesis by Th12;
end;
