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Theorem rpnnen2 15570
Description: The other half of rpnnen 15571, where we show an injection from sets of positive integers to real numbers. The obvious choice for this is binary expansion, but it has the unfortunate property that it does not produce an injection on numbers which end with all 0's or all 1's (the more well-known decimal version of this is 0.999... 15228). Instead, we opt for a ternary expansion, which produces (a scaled version of) the Cantor set. Since the Cantor set is riddled with gaps, we can show that any two sequences that are not equal must differ somewhere, and when they do, they are placed a finite distance apart, thus ensuring that the map is injective.

Our map assigns to each subset 𝐴 of the positive integers the number Σ𝑘𝐴(3↑-𝑘) = Σ𝑘 ∈ ℕ((𝐹𝐴)‘𝑘), where ((𝐹𝐴)‘𝑘) = if(𝑘𝐴, (3↑-𝑘), 0)) (rpnnen2lem1 15558). This is an infinite sum of real numbers (rpnnen2lem2 15559), and since 𝐴𝐵 implies (𝐹𝐴) ≤ (𝐹𝐵) (rpnnen2lem4 15561) and (𝐹‘ℕ) converges to 1 / 2 (rpnnen2lem3 15560) by geoisum1 15226, the sum is convergent to some real (rpnnen2lem5 15562 and rpnnen2lem6 15563) by the comparison test for convergence cvgcmp 15162. The comparison test also tells us that 𝐴𝐵 implies Σ(𝐹𝐴) ≤ Σ(𝐹𝐵) (rpnnen2lem7 15564).

Putting it all together, if we have two sets 𝑥𝑦, there must differ somewhere, and so there must be an 𝑚 such that 𝑛 < 𝑚(𝑛𝑥𝑛𝑦) but 𝑚 ∈ (𝑥𝑦) or vice versa. In this case, we split off the first 𝑚 − 1 terms (rpnnen2lem8 15565) and cancel them (rpnnen2lem10 15567), since these are the same for both sets. For the remaining terms, we use the subset property to establish that Σ(𝐹𝑦) ≤ Σ(𝐹‘(ℕ ∖ {𝑚})) and Σ(𝐹‘{𝑚}) ≤ Σ(𝐹𝑥) (where these sums are only over (ℤ𝑚)), and since Σ(𝐹‘(ℕ ∖ {𝑚})) = (3↑-𝑚) / 2 (rpnnen2lem9 15566) and Σ(𝐹‘{𝑚}) = (3↑-𝑚), we establish that Σ(𝐹𝑦) < Σ(𝐹𝑥) (rpnnen2lem11 15568) so that they must be different. By contraposition (rpnnen2lem12 15569), we find that this map is an injection. (Contributed by Mario Carneiro, 13-May-2013.) (Proof shortened by Mario Carneiro, 30-Apr-2014.) (Revised by NM, 17-Aug-2021.)

Assertion
Ref Expression
rpnnen2 𝒫 ℕ ≼ (0[,]1)

Proof of Theorem rpnnen2
Dummy variables 𝑥 𝑛 are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 eqid 2822 . 2 (𝑥 ∈ 𝒫 ℕ ↦ (𝑛 ∈ ℕ ↦ if(𝑛𝑥, ((1 / 3)↑𝑛), 0))) = (𝑥 ∈ 𝒫 ℕ ↦ (𝑛 ∈ ℕ ↦ if(𝑛𝑥, ((1 / 3)↑𝑛), 0)))
21rpnnen2lem12 15569 1 𝒫 ℕ ≼ (0[,]1)
Colors of variables: wff setvar class
Syntax hints:  ifcif 4439  𝒫 cpw 4511   class class class wbr 5042  cmpt 5122  (class class class)co 7140  cdom 8494  0cc0 10526  1c1 10527   / cdiv 11286  cn 11625  3c3 11681  [,]cicc 12729  cexp 13425
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1797  ax-4 1811  ax-5 1911  ax-6 1970  ax-7 2015  ax-8 2116  ax-9 2124  ax-10 2145  ax-11 2161  ax-12 2178  ax-ext 2794  ax-rep 5166  ax-sep 5179  ax-nul 5186  ax-pow 5243  ax-pr 5307  ax-un 7446  ax-inf2 9092  ax-cnex 10582  ax-resscn 10583  ax-1cn 10584  ax-icn 10585  ax-addcl 10586  ax-addrcl 10587  ax-mulcl 10588  ax-mulrcl 10589  ax-mulcom 10590  ax-addass 10591  ax-mulass 10592  ax-distr 10593  ax-i2m1 10594  ax-1ne0 10595  ax-1rid 10596  ax-rnegex 10597  ax-rrecex 10598  ax-cnre 10599  ax-pre-lttri 10600  ax-pre-lttrn 10601  ax-pre-ltadd 10602  ax-pre-mulgt0 10603  ax-pre-sup 10604
This theorem depends on definitions:  df-bi 210  df-an 400  df-or 845  df-3or 1085  df-3an 1086  df-tru 1541  df-fal 1551  df-ex 1782  df-nf 1786  df-sb 2070  df-mo 2622  df-eu 2653  df-clab 2801  df-cleq 2815  df-clel 2894  df-nfc 2962  df-ne 3012  df-nel 3116  df-ral 3135  df-rex 3136  df-reu 3137  df-rmo 3138  df-rab 3139  df-v 3471  df-sbc 3748  df-csb 3856  df-dif 3911  df-un 3913  df-in 3915  df-ss 3925  df-pss 3927  df-nul 4266  df-if 4440  df-pw 4513  df-sn 4540  df-pr 4542  df-tp 4544  df-op 4546  df-uni 4814  df-int 4852  df-iun 4896  df-br 5043  df-opab 5105  df-mpt 5123  df-tr 5149  df-id 5437  df-eprel 5442  df-po 5451  df-so 5452  df-fr 5491  df-se 5492  df-we 5493  df-xp 5538  df-rel 5539  df-cnv 5540  df-co 5541  df-dm 5542  df-rn 5543  df-res 5544  df-ima 5545  df-pred 6126  df-ord 6172  df-on 6173  df-lim 6174  df-suc 6175  df-iota 6293  df-fun 6336  df-fn 6337  df-f 6338  df-f1 6339  df-fo 6340  df-f1o 6341  df-fv 6342  df-isom 6343  df-riota 7098  df-ov 7143  df-oprab 7144  df-mpo 7145  df-om 7566  df-1st 7675  df-2nd 7676  df-wrecs 7934  df-recs 7995  df-rdg 8033  df-1o 8089  df-oadd 8093  df-er 8276  df-pm 8396  df-en 8497  df-dom 8498  df-sdom 8499  df-fin 8500  df-sup 8894  df-inf 8895  df-oi 8962  df-card 9356  df-pnf 10666  df-mnf 10667  df-xr 10668  df-ltxr 10669  df-le 10670  df-sub 10861  df-neg 10862  df-div 11287  df-nn 11626  df-2 11688  df-3 11689  df-n0 11886  df-z 11970  df-uz 12232  df-rp 12378  df-ico 12732  df-icc 12733  df-fz 12886  df-fzo 13029  df-fl 13157  df-seq 13365  df-exp 13426  df-hash 13687  df-cj 14449  df-re 14450  df-im 14451  df-sqrt 14585  df-abs 14586  df-limsup 14819  df-clim 14836  df-rlim 14837  df-sum 15034
This theorem is referenced by:  rpnnen  15571  opnreen  23434
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