 reserve n for Nat;

theorem THNOIX2:
  for p,q,r,s being Point of TarskiEuclid2Space st
    between p,q,r & between p,s,q holds between s,q,r
  proof
    let p,q,r,s be Point of TarskiEuclid2Space;
    assume that
A1: between p,q,r and
A2: between p,s,q;
A3: Tn2TR q in LSeg (Tn2TR p, Tn2TR r) by A1,ThConv6;
    Tn2TR s in LSeg (Tn2TR p, Tn2TR q) by A2,ThConv6;
    then Tn2TR q in LSeg(Tn2TR s, Tn2TR r) by A3,THNOIX;
    hence thesis by ThConv6;
  end;
