Either component of an outer disjunction may also be categorical, connected, or disjunctive. But reversing the verbal order of its two alternatives does not produce another basic structural class. Hence the total is six.
Same-type:
1. Categorical + categorical
2. Connected + connected
3. Disjunctive + disjunctive
Mixed:
4. Categorical + connected
5. Categorical + disjunctive
6. Connected + disjunctive
Thus 3 same-type + 3 mixed = 6. The connected total was nine because its two component positions have different roles.