theorem
  ex F being sequence of RAT st F is one-to-one & dom F = NAT & rng F = RAT
proof
  consider F being Function such that
A1: F is one-to-one and
A2: dom F = NAT & rng F = RAT by MESFUNC1:5,WELLORD2:def 4;
 F is sequence of RAT by A2,FUNCT_2:2;
  hence thesis by A1,A2;
end;
