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Theorem pm54.43 8434
 Description: Theorem *54.43 of [WhiteheadRussell] p. 360. "From this proposition it will follow, when arithmetical addition has been defined, that 1+1=2." See http://en.wikipedia.org/wiki/Principia_Mathematica#Quotations. This theorem states that two sets of cardinality 1 are disjoint iff their union has cardinality 2. Whitehead and Russell define 1 as the collection of all sets with cardinality 1 (i.e. all singletons; see card1 8402), so that their means, in our notation, which is the same as by pm54.43lem 8433. We do not have several of their earlier lemmas available (which would otherwise be unused by our different approach to arithmetic), so our proof is longer. (It is also longer because we must show every detail.) Theorem pm110.643 8607 shows the derivation of 1+1=2 for cardinal numbers from this theorem. (Contributed by NM, 4-Apr-2007.)
Assertion
Ref Expression
pm54.43

Proof of Theorem pm54.43
Dummy variables are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 1on 7189 . . . . . . . 8
21elexi 3055 . . . . . . 7
32ensn1 7633 . . . . . 6
43ensymi 7619 . . . . 5
5 entr 7621 . . . . 5
64, 5mpan2 677 . . . 4
71onirri 5529 . . . . . . 7
8 disjsn 4032 . . . . . . 7
97, 8mpbir 213 . . . . . 6
10 unen 7652 . . . . . 6
119, 10mpanr2 690 . . . . 5
1211ex 436 . . . 4
136, 12sylan2 477 . . 3
14 df-2o 7183 . . . . 5
15 df-suc 5429 . . . . 5
1614, 15eqtri 2473 . . . 4
1716breq2i 4410 . . 3
1813, 17syl6ibr 231 . 2
19 en1 7636 . . 3
20 en1 7636 . . 3
21 unidm 3577 . . . . . . . . . . . . . 14
22 sneq 3978 . . . . . . . . . . . . . . 15
2322uneq2d 3588 . . . . . . . . . . . . . 14
2421, 23syl5reqr 2500 . . . . . . . . . . . . 13
25 vex 3048 . . . . . . . . . . . . . . 15
2625ensn1 7633 . . . . . . . . . . . . . 14
27 1sdom2 7771 . . . . . . . . . . . . . 14
28 ensdomtr 7708 . . . . . . . . . . . . . 14
2926, 27, 28mp2an 678 . . . . . . . . . . . . 13
3024, 29syl6eqbr 4440 . . . . . . . . . . . 12
31 sdomnen 7598 . . . . . . . . . . . 12
3230, 31syl 17 . . . . . . . . . . 11
3332necon2ai 2653 . . . . . . . . . 10
34 disjsn2 4033 . . . . . . . . . 10
3533, 34syl 17 . . . . . . . . 9
3635a1i 11 . . . . . . . 8
37 uneq12 3583 . . . . . . . . 9
3837breq1d 4412 . . . . . . . 8
39 ineq12 3629 . . . . . . . . 9
4039eqeq1d 2453 . . . . . . . 8
4136, 38, 403imtr4d 272 . . . . . . 7
4241ex 436 . . . . . 6
4342exlimdv 1779 . . . . 5
4443exlimiv 1776 . . . 4
4544imp 431 . . 3
4619, 20, 45syl2anb 482 . 2
4718, 46impbid 194 1
 Colors of variables: wff setvar class Syntax hints:   wn 3   wi 4   wb 188   wa 371   wceq 1444  wex 1663   wcel 1887   wne 2622   cun 3402   cin 3403  c0 3731  csn 3968   class class class wbr 4402  con0 5423   csuc 5425  c1o 7175  c2o 7176   cen 7566   csdm 7568 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1669  ax-4 1682  ax-5 1758  ax-6 1805  ax-7 1851  ax-8 1889  ax-9 1896  ax-10 1915  ax-11 1920  ax-12 1933  ax-13 2091  ax-ext 2431  ax-sep 4525  ax-nul 4534  ax-pow 4581  ax-pr 4639  ax-un 6583 This theorem depends on definitions:  df-bi 189  df-or 372  df-an 373  df-3or 986  df-3an 987  df-tru 1447  df-ex 1664  df-nf 1668  df-sb 1798  df-eu 2303  df-mo 2304  df-clab 2438  df-cleq 2444  df-clel 2447  df-nfc 2581  df-ne 2624  df-ral 2742  df-rex 2743  df-reu 2744  df-rab 2746  df-v 3047  df-sbc 3268  df-dif 3407  df-un 3409  df-in 3411  df-ss 3418  df-pss 3420  df-nul 3732  df-if 3882  df-pw 3953  df-sn 3969  df-pr 3971  df-tp 3973  df-op 3975  df-uni 4199  df-br 4403  df-opab 4462  df-tr 4498  df-eprel 4745  df-id 4749  df-po 4755  df-so 4756  df-fr 4793  df-we 4795  df-xp 4840  df-rel 4841  df-cnv 4842  df-co 4843  df-dm 4844  df-rn 4845  df-res 4846  df-ima 4847  df-ord 5426  df-on 5427  df-lim 5428  df-suc 5429  df-iota 5546  df-fun 5584  df-fn 5585  df-f 5586  df-f1 5587  df-fo 5588  df-f1o 5589  df-fv 5590  df-om 6693  df-1o 7182  df-2o 7183  df-er 7363  df-en 7570  df-dom 7571  df-sdom 7572 This theorem is referenced by:  pr2nelem  8435  pm110.643  8607  isprm2lem  14631
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