unindex_vars (d, MIN (old_index, new_index), MAX (old_index, new_index) + 1);
move_element (d->vars, d->n_vars, sizeof *d->vars, old_index, new_index);
reindex_vars (d, MIN (old_index, new_index), MAX (old_index, new_index) + 1, false);
unindex_vars (d, MIN (old_index, new_index), MAX (old_index, new_index) + 1);
move_element (d->vars, d->n_vars, sizeof *d->vars, old_index, new_index);
reindex_vars (d, MIN (old_index, new_index), MAX (old_index, new_index) + 1, false);