for P, Q, R being Point of BK-model-Plane
for P2, Q2, R2 being POINT of TarskiEuclid2Space st P2 = BK_to_T2 P & Q2 = BK_to_T2 Q & R2 = BK_to_T2 R holds
( between P,Q,R iff between P2,Q2,R2 )