theorem Th32:
  not {A,B,C} is linear implies Plane(A,B,C) = Plane(C,A,B)
proof
  assume
A1: not {A,B,C} is linear;
  then
A2: not {C,A,B} is linear by ENUMSET1:59;
  thus Plane(A,B,C) = Plane(A,C,B) by A1,Th29
    .= Plane(C,A,B) by A2,Th30;
end;
