theorem Th9:
  for N,T
  for l1, l2 being Element of NAT holds locnum(l1,T) <=
  locnum(l2,T) iff l1 <= l2, T
proof let N,T;
  let l1, l2 be Element of NAT;
  il.(T,locnum(l1,T)) = l1 & il.(T,locnum(l2,T)) = l2 by Def5;
  hence thesis by Th8;
end;
