In the "wo" section, all of the labels are generated. In this case an XY grid. The unusual part is that there is no
cnf.write() call in this section. There are only calls to the grid function,
f(). Thus, this section of code does not actually generate any CNF information. However it does populate the
auto_term database. The write-only setting means that every call to
f() should be something new and never before seen. If the label is found to already exist in the database, then something is wrong. And in fact, it catches the duplicated X coordinate and complains about
Error: existing label (2,1). Change the extra 2 to a 3 and it'll get past that section. One bug found.