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 Satz8p5:
  right_angle a,b,b
  proof
    a,b equiv a,b by GTARSKI3:2;
    hence thesis by Lem01;
  end;
