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 Satz8p6:
  right_angle a,b,c & right_angle a9,b,c & between a,c,a9 implies b = c
  proof
    assume right_angle a,b,c & right_angle a9,b,c & between a,c,a9;
    then c = reflection(b,c) by GTARSKI3:55;
    hence thesis by GTARSKI3:104;
  end;
