 reserve n for Nat;

theorem
  for a,b,c,a1,b1,c1 being POINT of TarskiEuclid2Space holds
    a,b,c cong a1,b1,c1 iff (dist(a,b) = dist(a1,b1) &
    dist(a,c) = dist(a1,c1) & dist(b,c) = dist(b1,c1)) by GTARSKI1:def 15;
