  Consider a sequence of AG codes evaluating at a set of evaluation points
$P_1,\dots,P_n$ the functions having only poles at a defining point $Q$, with
the sequence of codes satisfying the isometry-dual condition (i.e. containing
at the same time primal and their dual codes). We prove a necessary condition
under which, after taking out a number of evaluation points (i.e. puncturing),
the resulting AG codes can still satisfy the isometry-dual property. The
condition has to do with the so-called maximum sparse ideals of the Weierstrass
semigroup of $Q$.
