I’ve just been checking these CU references, so thanks for that. One curious detail I’ve noticed. In SN 12.48 we have a brahmin lokāyatika who asks “does all exist”, and the Buddha rather curiously says “this is the eldest lokāyata”. Then “all does not exist” is the “second lokāyatika”.
Now, in CU 6.2 we have:
sad eva somyedam agra āsīd ekam evādvitīyam | tad dhaika āhur asad evedam agra āsīd ekam evādvitīyam | tasmād asataḥ saj jāyata || ChUp_6,2.1 ||
‘In the beginning,’ my dear, 'there was that only which is, one only, without a second. Others say, in the beginning there was that only which is not, one only, without a second; and from that which is not, that which is was born.
kutas tu khalu somyaivaṃ syād iti hovāca | katham asataḥ saj jāyeta | sat tv eva somyedam agra āsīd ekam evādvitīyam || ChUp_6,2.2 ||
‘But how could it be thus, my dear?’ the father continued. 'How could that which is, be born of that which is not? No, my dear, only that which is, was in the beginning, one only, without a second.
So the oldest theory of the origin of the world holds that there was existence, while the second theory holds there was non-existence. Coincidence?