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Theorem mgmidmo 17868
 Description: A two-sided identity element is unique (if it exists) in any magma. (Contributed by Mario Carneiro, 7-Dec-2014.) (Revised by NM, 17-Jun-2017.)
Assertion
Ref Expression
mgmidmo ∃*𝑢𝐵𝑥𝐵 ((𝑢 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑢) = 𝑥)
Distinct variable groups:   𝑥,𝑢,𝐵   𝑢, + ,𝑥

Proof of Theorem mgmidmo
Dummy variable 𝑤 is distinct from all other variables.
StepHypRef Expression
1 simpl 486 . . . . 5 (((𝑢 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑢) = 𝑥) → (𝑢 + 𝑥) = 𝑥)
21ralimi 3155 . . . 4 (∀𝑥𝐵 ((𝑢 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑢) = 𝑥) → ∀𝑥𝐵 (𝑢 + 𝑥) = 𝑥)
3 simpr 488 . . . . 5 (((𝑤 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑤) = 𝑥) → (𝑥 + 𝑤) = 𝑥)
43ralimi 3155 . . . 4 (∀𝑥𝐵 ((𝑤 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑤) = 𝑥) → ∀𝑥𝐵 (𝑥 + 𝑤) = 𝑥)
5 oveq1 7153 . . . . . . . . 9 (𝑥 = 𝑢 → (𝑥 + 𝑤) = (𝑢 + 𝑤))
6 id 22 . . . . . . . . 9 (𝑥 = 𝑢𝑥 = 𝑢)
75, 6eqeq12d 2840 . . . . . . . 8 (𝑥 = 𝑢 → ((𝑥 + 𝑤) = 𝑥 ↔ (𝑢 + 𝑤) = 𝑢))
87rspcva 3607 . . . . . . 7 ((𝑢𝐵 ∧ ∀𝑥𝐵 (𝑥 + 𝑤) = 𝑥) → (𝑢 + 𝑤) = 𝑢)
9 oveq2 7154 . . . . . . . . 9 (𝑥 = 𝑤 → (𝑢 + 𝑥) = (𝑢 + 𝑤))
10 id 22 . . . . . . . . 9 (𝑥 = 𝑤𝑥 = 𝑤)
119, 10eqeq12d 2840 . . . . . . . 8 (𝑥 = 𝑤 → ((𝑢 + 𝑥) = 𝑥 ↔ (𝑢 + 𝑤) = 𝑤))
1211rspcva 3607 . . . . . . 7 ((𝑤𝐵 ∧ ∀𝑥𝐵 (𝑢 + 𝑥) = 𝑥) → (𝑢 + 𝑤) = 𝑤)
138, 12sylan9req 2880 . . . . . 6 (((𝑢𝐵 ∧ ∀𝑥𝐵 (𝑥 + 𝑤) = 𝑥) ∧ (𝑤𝐵 ∧ ∀𝑥𝐵 (𝑢 + 𝑥) = 𝑥)) → 𝑢 = 𝑤)
1413an42s 660 . . . . 5 (((𝑢𝐵𝑤𝐵) ∧ (∀𝑥𝐵 (𝑢 + 𝑥) = 𝑥 ∧ ∀𝑥𝐵 (𝑥 + 𝑤) = 𝑥)) → 𝑢 = 𝑤)
1514ex 416 . . . 4 ((𝑢𝐵𝑤𝐵) → ((∀𝑥𝐵 (𝑢 + 𝑥) = 𝑥 ∧ ∀𝑥𝐵 (𝑥 + 𝑤) = 𝑥) → 𝑢 = 𝑤))
162, 4, 15syl2ani 609 . . 3 ((𝑢𝐵𝑤𝐵) → ((∀𝑥𝐵 ((𝑢 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑢) = 𝑥) ∧ ∀𝑥𝐵 ((𝑤 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑤) = 𝑥)) → 𝑢 = 𝑤))
1716rgen2 3198 . 2 𝑢𝐵𝑤𝐵 ((∀𝑥𝐵 ((𝑢 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑢) = 𝑥) ∧ ∀𝑥𝐵 ((𝑤 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑤) = 𝑥)) → 𝑢 = 𝑤)
18 oveq1 7153 . . . . 5 (𝑢 = 𝑤 → (𝑢 + 𝑥) = (𝑤 + 𝑥))
1918eqeq1d 2826 . . . 4 (𝑢 = 𝑤 → ((𝑢 + 𝑥) = 𝑥 ↔ (𝑤 + 𝑥) = 𝑥))
2019ovanraleqv 7170 . . 3 (𝑢 = 𝑤 → (∀𝑥𝐵 ((𝑢 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑢) = 𝑥) ↔ ∀𝑥𝐵 ((𝑤 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑤) = 𝑥)))
2120rmo4 3707 . 2 (∃*𝑢𝐵𝑥𝐵 ((𝑢 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑢) = 𝑥) ↔ ∀𝑢𝐵𝑤𝐵 ((∀𝑥𝐵 ((𝑢 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑢) = 𝑥) ∧ ∀𝑥𝐵 ((𝑤 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑤) = 𝑥)) → 𝑢 = 𝑤))
2217, 21mpbir 234 1 ∃*𝑢𝐵𝑥𝐵 ((𝑢 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑢) = 𝑥)
 Colors of variables: wff setvar class Syntax hints:   → wi 4   ∧ wa 399   = wceq 1538   ∈ wcel 2115  ∀wral 3133  ∃*wrmo 3136  (class class class)co 7146 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 1912  ax-6 1971  ax-7 2016  ax-8 2117  ax-9 2125  ax-ext 2796 This theorem depends on definitions:  df-bi 210  df-an 400  df-or 845  df-3an 1086  df-ex 1782  df-sb 2071  df-mo 2624  df-clab 2803  df-cleq 2817  df-clel 2896  df-ral 3138  df-rmo 3141  df-v 3482  df-un 3924  df-in 3926  df-ss 3936  df-sn 4551  df-pr 4553  df-op 4557  df-uni 4826  df-br 5054  df-iota 6303  df-fv 6352  df-ov 7149 This theorem is referenced by:  ismgmid  17873  mndideu  17920
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