theorem
  for il being Nat, dl being FinSeq-Location
  holds il <> dl
proof
  let il be Nat, dl be FinSeq-Location;
A1: dl in INT \ NAT by Def3;
A2: il in NAT by ORDINAL1:def 12;
   NAT misses INT \ NAT by XBOOLE_1:79;
 hence thesis by A1,A2,XBOOLE_0:3;
end;
