Theorem rpnnen2 16105

Description: The other half of rpnnen 16106, 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... 15763). 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 Σ𝑘 ∈ 𝐴(3↑-𝑘) = Σ𝑘 ∈ ℕ((𝐹‘𝐴)‘𝑘), where ((𝐹‘𝐴)‘𝑘) = if(𝑘 ∈ 𝐴, (3↑-𝑘), 0)) (rpnnen2lem1 16093). This is an infinite sum of real numbers (rpnnen2lem2 16094), and since 𝐴 ⊆ 𝐵 implies (𝐹‘𝐴) ≤ (𝐹‘𝐵) (rpnnen2lem4 16096) and (𝐹‘ℕ) converges to 1 / 2 (rpnnen2lem3 16095) by geoisum1 15761, the sum is convergent to some real (rpnnen2lem5 16097 and rpnnen2lem6 16098) by the comparison test for convergence cvgcmp 15698. The comparison test also tells us that 𝐴 ⊆ 𝐵 implies Σ(𝐹‘𝐴) ≤ Σ(𝐹‘𝐵) (rpnnen2lem7 16099).

Putting it all together, if we have two sets 𝑥 ≠ 𝑦, there must differ somewhere, and so there must be an 𝑚 such that ∀𝑛 < 𝑚(𝑛 ∈ 𝑥 ↔ 𝑛 ∈ 𝑦) but 𝑚 ∈ (𝑥 ∖ 𝑦) or vice versa. In this case, we split off the first 𝑚 − 1 terms (rpnnen2lem8 16100) and cancel them (rpnnen2lem10 16102), since these are the same for both sets. For the remaining terms, we use the subset property to establish that Σ(𝐹‘𝑦) ≤ Σ(𝐹‘(ℕ ∖ {𝑚})) and Σ(𝐹‘{𝑚}) ≤ Σ(𝐹‘𝑥) (where these sums are only over (ℤ_≥‘𝑚)), and since Σ(𝐹‘(ℕ ∖ {𝑚})) = (3↑-𝑚) / 2 (rpnnen2lem9 16101) and Σ(𝐹‘{𝑚}) = (3↑-𝑚), we establish that Σ(𝐹‘𝑦) < Σ(𝐹‘𝑥) (rpnnen2lem11 16103) so that they must be different. By contraposition (rpnnen2lem12 16104), 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.

Step	Hyp	Ref	Expression
1		eqid 2736	. 2 ⊢ (𝑥 ∈ 𝒫 ℕ ↦ (𝑛 ∈ ℕ ↦ if(𝑛 ∈ 𝑥, ((1 / 3)↑𝑛), 0))) = (𝑥 ∈ 𝒫 ℕ ↦ (𝑛 ∈ ℕ ↦ if(𝑛 ∈ 𝑥, ((1 / 3)↑𝑛), 0)))
2	1	rpnnen2lem12 16104	1 ⊢ 𝒫 ℕ ≼ (0[,]1)

Syntax hints:  ifcif 4485  𝒫 cpw 4559   class class class wbr 5104   ↦ cmpt 5187  (class class class)co 7354   ≼ cdom 8878  0cc0 11048  1c1 11049   / cdiv 11809  ℕcn 12150  3c3 12206  [,]cicc 13264  ↑cexp 13964

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 1913  ax-6 1971  ax-7 2011  ax-8 2108  ax-9 2116  ax-10 2137  ax-11 2154  ax-12 2171  ax-ext 2707  ax-rep 5241  ax-sep 5255  ax-nul 5262  ax-pow 5319  ax-pr 5383  ax-un 7669  ax-inf2 9574  ax-cnex 11104  ax-resscn 11105  ax-1cn 11106  ax-icn 11107  ax-addcl 11108  ax-addrcl 11109  ax-mulcl 11110  ax-mulrcl 11111  ax-mulcom 11112  ax-addass 11113  ax-mulass 11114  ax-distr 11115  ax-i2m1 11116  ax-1ne0 11117  ax-1rid 11118  ax-rnegex 11119  ax-rrecex 11120  ax-cnre 11121  ax-pre-lttri 11122  ax-pre-lttrn 11123  ax-pre-ltadd 11124  ax-pre-mulgt0 11125  ax-pre-sup 11126

This theorem depends on definitions:  df-bi 206  df-an 397  df-or 846  df-3or 1088  df-3an 1089  df-tru 1544  df-fal 1554  df-ex 1782  df-nf 1786  df-sb 2068  df-mo 2538  df-eu 2567  df-clab 2714  df-cleq 2728  df-clel 2814  df-nfc 2888  df-ne 2943  df-nel 3049  df-ral 3064  df-rex 3073  df-rmo 3352  df-reu 3353  df-rab 3407  df-v 3446  df-sbc 3739  df-csb 3855  df-dif 3912  df-un 3914  df-in 3916  df-ss 3926  df-pss 3928  df-nul 4282  df-if 4486  df-pw 4561  df-sn 4586  df-pr 4588  df-op 4592  df-uni 4865  df-int 4907  df-iun 4955  df-br 5105  df-opab 5167  df-mpt 5188  df-tr 5222  df-id 5530  df-eprel 5536  df-po 5544  df-so 5545  df-fr 5587  df-se 5588  df-we 5589  df-xp 5638  df-rel 5639  df-cnv 5640  df-co 5641  df-dm 5642  df-rn 5643  df-res 5644  df-ima 5645  df-pred 6252  df-ord 6319  df-on 6320  df-lim 6321  df-suc 6322  df-iota 6446  df-fun 6496  df-fn 6497  df-f 6498  df-f1 6499  df-fo 6500  df-f1o 6501  df-fv 6502  df-isom 6503  df-riota 7310  df-ov 7357  df-oprab 7358  df-mpo 7359  df-om 7800  df-1st 7918  df-2nd 7919  df-frecs 8209  df-wrecs 8240  df-recs 8314  df-rdg 8353  df-1o 8409  df-er 8645  df-pm 8765  df-en 8881  df-dom 8882  df-sdom 8883  df-fin 8884  df-sup 9375  df-inf 9376  df-oi 9443  df-card 9872  df-pnf 11188  df-mnf 11189  df-xr 11190  df-ltxr 11191  df-le 11192  df-sub 11384  df-neg 11385  df-div 11810  df-nn 12151  df-2 12213  df-3 12214  df-n0 12411  df-z 12497  df-uz 12761  df-rp 12913  df-ico 13267  df-icc 13268  df-fz 13422  df-fzo 13565  df-fl 13694  df-seq 13904  df-exp 13965  df-hash 14228  df-cj 14981  df-re 14982  df-im 14983  df-sqrt 15117  df-abs 15118  df-limsup 15350  df-clim 15367  df-rlim 15368  df-sum 15568

This theorem is referenced by:  rpnnen  16106  opnreen  24190