reserve n for Element of NAT,
  p,q,r,s for Element of HP-WFF;

theorem Th11:
  for D being non empty set for f being Function of 2, D ex d1,d2
  being Element of D st f = (0,1) --> (d1,d2)
proof
  let D be non empty set;
  let f be Function of 2, D;
  0 in 2 & 1 in 2 by CARD_1:50,TARSKI:def 2;
  then reconsider d1 = f.0, d2 = f.1 as Element of D by FUNCT_2:5;
  take d1,d2;
  dom f = {0,1} by CARD_1:50,FUNCT_2:def 1;
  hence thesis by FUNCT_4:66;
end;
