theorem Satz3p2:
  between a,b,c implies between c,b,a
  proof
    assume
A1: between a,b,c;
    between b,c,c by Satz3p1;
    then ex x be POINT of S st between b,x,b & between c,x,a
      by A1,GTARSKI1:def 11;
    hence thesis by GTARSKI1:def 10;
  end;
