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 Satz8p8:
  right_angle a,b,a implies a = b
  proof
    assume
A1: right_angle a,b,a;
    right_angle a,a,b by Satz8p2,Satz8p5;
    hence thesis by A1,Satz8p7;
  end;
