reserve S for non empty satisfying_Tarski-model
              TarskiGeometryStruct,
        a,b,c,d,c9,x,y,z,p,q,q9 for POINT of S;
reserve              S for satisfying_Tarski-model TarskiGeometryStruct,
        a,a9,b,b9,c,c9 for POINT of S;

theorem
  right_angle a,b,c implies right_angle a,b,reflection(b,c)
  proof
    assume right_angle a,b,c;
    then a,reflection(b,c) equiv a,c by GTARSKI3:4;
    hence thesis by GTARSKI3:101;
  end;
