theorem Th42:
  [0,1,0] is Element of EC_SetProjCo(a,b,p)
  proof
    [0,1,0] is Element of ProjCo(GF(p))
    & EC_WEqProjCo(a,b,p).([0,1,0]) = 0.GF(p) by Lm5;
    then [0,1,0] in {P where P is Element of ProjCo(GF(p)) :
    EC_WEqProjCo(a,b,p).P = 0.GF(p)};
    hence thesis;
  end;
