 reserve S for satisfying_Tarski-model TarskiGeometryStruct;
 reserve a, b, c, d, e, f, o, p, q, r, s,
    v, w, u, x, y, z, a9, b9, c9, d9, x9, y9, z for POINT of S;

theorem A4:
  ex x st between q,a,x & a,x equiv b,c
  proof
    S is satisfying_SegmentConstruction;
    hence thesis;
  end;
