Description: Lemma for pwfseq . Although in some ways pwfseqlem4 is the "main" part of the proof, one last aspect which makes up a remark in the original text is by far the hardest part to formalize. The main proof relies on the existence of an injection K from the set of finite sequences on an infinite set x to x . Now this alone would not be difficult to prove; this is mostly the claim of fseqen . However, what is needed for the proof is acanonical injection on these sets, so we have to start from scratch pulling together explicit bijections from the lemmas.
If one attempts such a program, it will mostly go through, but there is one key step which is inherently nonconstructive, namely the proof of infxpen . The resolution is not obvious, but it turns out that reversing an infinite ordinal's Cantor normal form absorbs all the non-leading terms ( cnfcom3c ), which can be used to construct a pairing function explicitly using properties of the ordinal exponential ( infxpenc ). (Contributed by Mario Carneiro, 31-May-2015)
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Hypotheses | pwfseqlem5.g | |
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pwfseqlem5.x | |
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pwfseqlem5.h | |
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pwfseqlem5.ps | |
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pwfseqlem5.n | |
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pwfseqlem5.o | |
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pwfseqlem5.t | |
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pwfseqlem5.p | |
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pwfseqlem5.s | |
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pwfseqlem5.q | |
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pwfseqlem5.i | |
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pwfseqlem5.k | |
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Assertion | pwfseqlem5 | |