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Theorem diftpsn3OLD 4478
 Description: Obsolete proof of diftpsn3 4477 as of 23-Jul-2021. (Contributed by Alexander van der Vekens, 5-Oct-2017.) (New usage is discouraged.) (Proof modification is discouraged.)
Assertion
Ref Expression
diftpsn3OLD ((𝐴𝐶𝐵𝐶) → ({𝐴, 𝐵, 𝐶} ∖ {𝐶}) = {𝐴, 𝐵})

Proof of Theorem diftpsn3OLD
StepHypRef Expression
1 df-tp 4326 . . . 4 {𝐴, 𝐵, 𝐶} = ({𝐴, 𝐵} ∪ {𝐶})
21a1i 11 . . 3 ((𝐴𝐶𝐵𝐶) → {𝐴, 𝐵, 𝐶} = ({𝐴, 𝐵} ∪ {𝐶}))
32difeq1d 3870 . 2 ((𝐴𝐶𝐵𝐶) → ({𝐴, 𝐵, 𝐶} ∖ {𝐶}) = (({𝐴, 𝐵} ∪ {𝐶}) ∖ {𝐶}))
4 difundir 4023 . . 3 (({𝐴, 𝐵} ∪ {𝐶}) ∖ {𝐶}) = (({𝐴, 𝐵} ∖ {𝐶}) ∪ ({𝐶} ∖ {𝐶}))
54a1i 11 . 2 ((𝐴𝐶𝐵𝐶) → (({𝐴, 𝐵} ∪ {𝐶}) ∖ {𝐶}) = (({𝐴, 𝐵} ∖ {𝐶}) ∪ ({𝐶} ∖ {𝐶})))
6 df-pr 4324 . . . . . . . . 9 {𝐴, 𝐵} = ({𝐴} ∪ {𝐵})
76a1i 11 . . . . . . . 8 ((𝐴𝐶𝐵𝐶) → {𝐴, 𝐵} = ({𝐴} ∪ {𝐵}))
87ineq1d 3956 . . . . . . 7 ((𝐴𝐶𝐵𝐶) → ({𝐴, 𝐵} ∩ {𝐶}) = (({𝐴} ∪ {𝐵}) ∩ {𝐶}))
9 incom 3948 . . . . . . . . 9 (({𝐴} ∪ {𝐵}) ∩ {𝐶}) = ({𝐶} ∩ ({𝐴} ∪ {𝐵}))
10 indi 4016 . . . . . . . . 9 ({𝐶} ∩ ({𝐴} ∪ {𝐵})) = (({𝐶} ∩ {𝐴}) ∪ ({𝐶} ∩ {𝐵}))
119, 10eqtri 2782 . . . . . . . 8 (({𝐴} ∪ {𝐵}) ∩ {𝐶}) = (({𝐶} ∩ {𝐴}) ∪ ({𝐶} ∩ {𝐵}))
1211a1i 11 . . . . . . 7 ((𝐴𝐶𝐵𝐶) → (({𝐴} ∪ {𝐵}) ∩ {𝐶}) = (({𝐶} ∩ {𝐴}) ∪ ({𝐶} ∩ {𝐵})))
13 necom 2985 . . . . . . . . . . 11 (𝐴𝐶𝐶𝐴)
14 disjsn2 4391 . . . . . . . . . . 11 (𝐶𝐴 → ({𝐶} ∩ {𝐴}) = ∅)
1513, 14sylbi 207 . . . . . . . . . 10 (𝐴𝐶 → ({𝐶} ∩ {𝐴}) = ∅)
1615adantr 472 . . . . . . . . 9 ((𝐴𝐶𝐵𝐶) → ({𝐶} ∩ {𝐴}) = ∅)
17 necom 2985 . . . . . . . . . . 11 (𝐵𝐶𝐶𝐵)
18 disjsn2 4391 . . . . . . . . . . 11 (𝐶𝐵 → ({𝐶} ∩ {𝐵}) = ∅)
1917, 18sylbi 207 . . . . . . . . . 10 (𝐵𝐶 → ({𝐶} ∩ {𝐵}) = ∅)
2019adantl 473 . . . . . . . . 9 ((𝐴𝐶𝐵𝐶) → ({𝐶} ∩ {𝐵}) = ∅)
2116, 20uneq12d 3911 . . . . . . . 8 ((𝐴𝐶𝐵𝐶) → (({𝐶} ∩ {𝐴}) ∪ ({𝐶} ∩ {𝐵})) = (∅ ∪ ∅))
22 unidm 3899 . . . . . . . 8 (∅ ∪ ∅) = ∅
2321, 22syl6eq 2810 . . . . . . 7 ((𝐴𝐶𝐵𝐶) → (({𝐶} ∩ {𝐴}) ∪ ({𝐶} ∩ {𝐵})) = ∅)
248, 12, 233eqtrd 2798 . . . . . 6 ((𝐴𝐶𝐵𝐶) → ({𝐴, 𝐵} ∩ {𝐶}) = ∅)
25 disj3 4164 . . . . . 6 (({𝐴, 𝐵} ∩ {𝐶}) = ∅ ↔ {𝐴, 𝐵} = ({𝐴, 𝐵} ∖ {𝐶}))
2624, 25sylib 208 . . . . 5 ((𝐴𝐶𝐵𝐶) → {𝐴, 𝐵} = ({𝐴, 𝐵} ∖ {𝐶}))
2726eqcomd 2766 . . . 4 ((𝐴𝐶𝐵𝐶) → ({𝐴, 𝐵} ∖ {𝐶}) = {𝐴, 𝐵})
28 difid 4091 . . . . 5 ({𝐶} ∖ {𝐶}) = ∅
2928a1i 11 . . . 4 ((𝐴𝐶𝐵𝐶) → ({𝐶} ∖ {𝐶}) = ∅)
3027, 29uneq12d 3911 . . 3 ((𝐴𝐶𝐵𝐶) → (({𝐴, 𝐵} ∖ {𝐶}) ∪ ({𝐶} ∖ {𝐶})) = ({𝐴, 𝐵} ∪ ∅))
31 un0 4110 . . 3 ({𝐴, 𝐵} ∪ ∅) = {𝐴, 𝐵}
3230, 31syl6eq 2810 . 2 ((𝐴𝐶𝐵𝐶) → (({𝐴, 𝐵} ∖ {𝐶}) ∪ ({𝐶} ∖ {𝐶})) = {𝐴, 𝐵})
333, 5, 323eqtrd 2798 1 ((𝐴𝐶𝐵𝐶) → ({𝐴, 𝐵, 𝐶} ∖ {𝐶}) = {𝐴, 𝐵})
 Colors of variables: wff setvar class Syntax hints:   → wi 4   ∧ wa 383   = wceq 1632   ≠ wne 2932   ∖ cdif 3712   ∪ cun 3713   ∩ cin 3714  ∅c0 4058  {csn 4321  {cpr 4323  {ctp 4325 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1871  ax-4 1886  ax-5 1988  ax-6 2054  ax-7 2090  ax-9 2148  ax-10 2168  ax-11 2183  ax-12 2196  ax-13 2391  ax-ext 2740 This theorem depends on definitions:  df-bi 197  df-or 384  df-an 385  df-tru 1635  df-ex 1854  df-nf 1859  df-sb 2047  df-clab 2747  df-cleq 2753  df-clel 2756  df-nfc 2891  df-ne 2933  df-ral 3055  df-rab 3059  df-v 3342  df-dif 3718  df-un 3720  df-in 3722  df-ss 3729  df-nul 4059  df-sn 4322  df-pr 4324  df-tp 4326 This theorem is referenced by: (None)
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