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
  for p1,p2 st p1<>p2 or p1-p2<>0.TOP-REAL 2 holds (Arg(p1-p2)<PI iff
  Arg(p2-p1)>=PI)
proof
  let p1,p2;
  assume p1<>p2 or p1-p2<>0.TOP-REAL 2;
  then
A1: p1-p2<>0.TOP-REAL 2 by RLVECT_1:21;
  -(p1-p2)=p2-p1 by RLVECT_1:33;
  hence thesis by A1,Th31;
end;
