3.
Commentary on the Chapter on With Sign
78-79. In the first of the third, "with a sign" means with a cause. The same method applies also to the second and so on. Source, cause, activity, condition, matter - for all these are indeed synonyms for reason.
84. In the seventh, "with feeling" means they arise only when there is feeling associated with and become the condition for them, not when it is absent - this is the meaning. The same method applies to the eighth and ninth as well.
87. In the tenth, "with the conditioned as object" means they arise only having made as object conditioned phenomena produced by conditions. "Not with the unconditioned as object" means they do not arise referring to the unconditioned, Nibbāna. "Do not exist" means they are said not to exist at the moment of the path; when the fruition is attained, they did not exist. Thus in all these ten states, the teaching has been taught up to arahantship.
The Chapter on With Sign is the third.