theorem
  for p be Prime, a, b, Px, Py, Pz be Element of GF(p),
  P be Element of EC_SetProjCo(a,b,p) st P = [Px, Py, Pz]
  holds P`1_3 = Px & P`2_3 = Py & P`3_3 = Pz by Def3,Def4,Def5;
