An epsilon number is a transfinite number which is a fixed point of an exponential map: ωϵ = ϵ. The formalization of the concept is done with use of the tetration of ordinals (Knuth's arrow notation, ↑). Namely, the ordinal indexing of epsilon numbers is defined as follows: [...] and for limit ordinal λ: [...] Tetration stabilizes at ω: [...] Every ordinal number α can be uniquely written as [...] where κ is a natural number, n1, n2, …, nk are positive integers, and β1 > β2 > … > βκ are ordinal numbers (βκ = 0). This decomposition of α is called the Cantor Normal Form of α.
@article{bwmeta1.element.doi-10_2478_v10037-009-0032-8, author = {Grzegorz Bancerek}, title = {Epsilon Numbers and Cantor Normal Form}, journal = {Formalized Mathematics}, volume = {17}, year = {2009}, pages = {249-256}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.doi-10_2478_v10037-009-0032-8} }
Grzegorz Bancerek. Epsilon Numbers and Cantor Normal Form. Formalized Mathematics, Tome 17 (2009) pp. 249-256. http://gdmltest.u-ga.fr/item/bwmeta1.element.doi-10_2478_v10037-009-0032-8/
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