Comm. NT: 16.
Paṭṭhānapaccayakathāvaṇṇanā
... “The presence (atthi) condition is not applicable to Nibbāna.
For a presence condition is that which is unhelpful by its absence of existingness (atthi-bhāvābhāva) and becomes helpful by obtaining existingness.
And Nibbāna does not, after being unhelpful by its own absence of existingness to those states that have Nibbāna as their object, become helpful to them by obtaining existingness. Or alternatively, the presence condition, which by its non-existingness is the opposite of helpfulness to those states that are associated with arising, etc., is helpful to them by its existingness. So Nibbāna is not a presence condition”
It may be noted that atthi has more than one use, among which the following two may be mentioned: (1) atthi (is) = upalabbhaniya (is (a) “apprehendable,” and (b) not a self-contradictory impossibility)—“atthi, bhikkhave, ajātaṃ—There is an unborn' (Ud 80), and the discussion on the existence of Nibbāna (XVI.67ff.). (2) Atthi (is) = uppanna (arisen)—see “Yaṃ, bhikkhave, rūpaṃ jātaṃ pātubhūtaṃ atthī ti tassa saṅkhā—Of the materiality that is born, manifested, it is said that ‘It is’” (S II 71f.). The atthi-paccaya (presence condition), being implicitly equated with the latter, cannot be applied to Nibbāna because Nibbāna is not subject to arising (A I 152).