$title use and misuse of dynamic sets

set 
    i/1*1000/
    j(i)
    k(i,i)
    l(i,i) /1*10 . 1*10/
    m(i) /1*10, 20*30/;

* define j to be a dynamic set - the first 300 elements of i
j(i)$(ord(i) < 300) = yes;

* k a dynamic set also - the cartesian product of i and j
k(i,j) = yes;

scalar n, val;

* card() operation legal for both static and dynamic sets
n = card(j); display n;
n = card(k); display n;
n = card(l); display n;

* ord() operation valid only for static sets; by using it here we are
* establishing m as a static set
loop(m,
	val = ord(m); display val;
);

* the following assignment requires m to be dynamic and is disallowed, 
* since it has already been established as a static set.
m('40') = yes;

* the following statement doesn't work, since ord() is not defined on a
* dynamic set, and we have established j as dynamic above
loop(j,
	val = ord(j);
	display val;
);