User blog comment:KthulhuHimself/Ordinal Arithmetic Notation (OAN)/@comment-34422464-20191112192546/@comment-37246647-20191114034257

Kthulhu, phi(0,a) is equal to w^a if a is smaller than epsilon-naught or a successor ordinal, or it's equal to a if a is epsilon-naught or a limit ordinal that is larger than epsilon-naught.