theorem
  for X1,X2 being non empty set,
        cF1 being Filter of X1,
        cF2 being Filter of X2,
          Y being Hausdorff regular non empty TopSpace,
          f being Function of [:X1,X2:],Y
  st lim_filter(f,<.cF1,cF2.)) <> {} &
     (for x being Element of X1 holds lim_filter(ProjMap1(f,x),cF2) <> {}) &
     (for x being Element of X2 holds lim_filter(ProjMap2(f,x),cF1) <> {})
  holds
  lim_filter(lim_in_cod2(f,cF2),cF1)
    = lim_filter(lim_in_cod1(f,cF1),cF2)
  proof
    let X1,X2 be non empty set,
    cF1 be Filter of X1,
    cF2 be Filter of X2,
    Y be Hausdorff regular non empty TopSpace,
    f be Function of [:X1,X2:],Y;
    assume that
A1: lim_filter(f,<.cF1,cF2.)) <> {} and
A2: (for x being Element of X1 holds
      lim_filter(ProjMap1(f,x),cF2) <> {}) and
A3: (for x being Element of X2 holds
      lim_filter(ProjMap2(f,x),cF1) <> {});
    lim_filter(f,<.cF1,cF2.)) = lim_filter(lim_in_cod1(f,cF1),cF2)
      by A1,A3,Th81;
    hence thesis by A1,A2,Th80;
  end;
