rem: assert (file == 0 ? field < 0 : field >= 0);
add: assert (file != 0 || field == 0);
context: add_field (int file, int field){  struct outlist *o;  assert (file == 0 || file == 1 || file == 2);  assert (file == 0 ? field < 0 : field >= 0);  o = (struct outlist *) xmalloc (sizeof (struct outlist));  o->file = file;  o->field = field;  o->next = NULL;  /* Add to the end of the list so the fields are in the right order.  */  outlist_end->next = o;  outlist_end = o;}