Dear Lennart,
thank you very much for the helps and answers.

I read somewhere (The manuals of Dhamma, by Ledi Sayadaw) another use of the two terms:
Sotaapannas attain saupaadisesa-nibbaana and will still have births (i.e. with the Groups of existence still remaining) until they die as arahats, then they attain anupaadisesa-nibbaana.
This makes more sense now if Sotapaana does experience nibbaana.

Virtually with real metta,
yufen



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