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Theorem sgrpidmnd 17916
 Description: A semigroup with an identity element which is not the empty set is a monoid. Of course there could be monoids with the empty set as identity element (see, for example, the monoid of the power set of a class under union, pwmnd 18102 and pwmndid 18101), but these cannot be proven to be monoids with this theorem. (Contributed by AV, 29-Jan-2024.)
Hypotheses
Ref Expression
sgrpidmnd.b 𝐵 = (Base‘𝐺)
sgrpidmnd.0 0 = (0g𝐺)
Assertion
Ref Expression
sgrpidmnd ((𝐺 ∈ Smgrp ∧ ∃𝑒𝐵 (𝑒 ≠ ∅ ∧ 𝑒 = 0 )) → 𝐺 ∈ Mnd)
Distinct variable groups:   𝐵,𝑒   𝑒,𝐺
Allowed substitution hint:   0 (𝑒)

Proof of Theorem sgrpidmnd
Dummy variables 𝑥 𝑦 are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 sgrpidmnd.b . . . . . . . . . 10 𝐵 = (Base‘𝐺)
2 eqid 2824 . . . . . . . . . 10 (+g𝐺) = (+g𝐺)
3 sgrpidmnd.0 . . . . . . . . . 10 0 = (0g𝐺)
41, 2, 3grpidval 17871 . . . . . . . . 9 0 = (℩𝑦(𝑦𝐵 ∧ ∀𝑥𝐵 ((𝑦(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑦) = 𝑥)))
54eqeq2i 2837 . . . . . . . 8 (𝑒 = 0𝑒 = (℩𝑦(𝑦𝐵 ∧ ∀𝑥𝐵 ((𝑦(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑦) = 𝑥))))
6 eleq1w 2898 . . . . . . . . . . . . 13 (𝑦 = 𝑒 → (𝑦𝐵𝑒𝐵))
7 oveq1 7156 . . . . . . . . . . . . . . 15 (𝑦 = 𝑒 → (𝑦(+g𝐺)𝑥) = (𝑒(+g𝐺)𝑥))
87eqeq1d 2826 . . . . . . . . . . . . . 14 (𝑦 = 𝑒 → ((𝑦(+g𝐺)𝑥) = 𝑥 ↔ (𝑒(+g𝐺)𝑥) = 𝑥))
98ovanraleqv 7173 . . . . . . . . . . . . 13 (𝑦 = 𝑒 → (∀𝑥𝐵 ((𝑦(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑦) = 𝑥) ↔ ∀𝑥𝐵 ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥)))
106, 9anbi12d 633 . . . . . . . . . . . 12 (𝑦 = 𝑒 → ((𝑦𝐵 ∧ ∀𝑥𝐵 ((𝑦(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑦) = 𝑥)) ↔ (𝑒𝐵 ∧ ∀𝑥𝐵 ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥))))
1110iotan0 6333 . . . . . . . . . . 11 ((𝑒𝐵𝑒 ≠ ∅ ∧ 𝑒 = (℩𝑦(𝑦𝐵 ∧ ∀𝑥𝐵 ((𝑦(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑦) = 𝑥)))) → (𝑒𝐵 ∧ ∀𝑥𝐵 ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥)))
12 rsp 3200 . . . . . . . . . . 11 (∀𝑥𝐵 ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥) → (𝑥𝐵 → ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥)))
1311, 12simpl2im 507 . . . . . . . . . 10 ((𝑒𝐵𝑒 ≠ ∅ ∧ 𝑒 = (℩𝑦(𝑦𝐵 ∧ ∀𝑥𝐵 ((𝑦(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑦) = 𝑥)))) → (𝑥𝐵 → ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥)))
14133expb 1117 . . . . . . . . 9 ((𝑒𝐵 ∧ (𝑒 ≠ ∅ ∧ 𝑒 = (℩𝑦(𝑦𝐵 ∧ ∀𝑥𝐵 ((𝑦(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑦) = 𝑥))))) → (𝑥𝐵 → ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥)))
1514expcom 417 . . . . . . . 8 ((𝑒 ≠ ∅ ∧ 𝑒 = (℩𝑦(𝑦𝐵 ∧ ∀𝑥𝐵 ((𝑦(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑦) = 𝑥)))) → (𝑒𝐵 → (𝑥𝐵 → ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥))))
165, 15sylan2b 596 . . . . . . 7 ((𝑒 ≠ ∅ ∧ 𝑒 = 0 ) → (𝑒𝐵 → (𝑥𝐵 → ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥))))
1716impcom 411 . . . . . 6 ((𝑒𝐵 ∧ (𝑒 ≠ ∅ ∧ 𝑒 = 0 )) → (𝑥𝐵 → ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥)))
1817ralrimiv 3176 . . . . 5 ((𝑒𝐵 ∧ (𝑒 ≠ ∅ ∧ 𝑒 = 0 )) → ∀𝑥𝐵 ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥))
1918ex 416 . . . 4 (𝑒𝐵 → ((𝑒 ≠ ∅ ∧ 𝑒 = 0 ) → ∀𝑥𝐵 ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥)))
2019reximia 3236 . . 3 (∃𝑒𝐵 (𝑒 ≠ ∅ ∧ 𝑒 = 0 ) → ∃𝑒𝐵𝑥𝐵 ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥))
2120anim2i 619 . 2 ((𝐺 ∈ Smgrp ∧ ∃𝑒𝐵 (𝑒 ≠ ∅ ∧ 𝑒 = 0 )) → (𝐺 ∈ Smgrp ∧ ∃𝑒𝐵𝑥𝐵 ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥)))
221, 2ismnddef 17913 . 2 (𝐺 ∈ Mnd ↔ (𝐺 ∈ Smgrp ∧ ∃𝑒𝐵𝑥𝐵 ((𝑒(+g𝐺)𝑥) = 𝑥 ∧ (𝑥(+g𝐺)𝑒) = 𝑥)))
2321, 22sylibr 237 1 ((𝐺 ∈ Smgrp ∧ ∃𝑒𝐵 (𝑒 ≠ ∅ ∧ 𝑒 = 0 )) → 𝐺 ∈ Mnd)
 Colors of variables: wff setvar class Syntax hints:   → wi 4   ∧ wa 399   ∧ w3a 1084   = wceq 1538   ∈ wcel 2115   ≠ wne 3014  ∀wral 3133  ∃wrex 3134  ∅c0 4276  ℩cio 6300  ‘cfv 6343  (class class class)co 7149  Basecbs 16483  +gcplusg 16565  0gc0g 16713  Smgrpcsgrp 17900  Mndcmnd 17911 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-10 2146  ax-11 2162  ax-12 2179  ax-ext 2796  ax-sep 5189  ax-nul 5196  ax-pow 5253  ax-pr 5317 This theorem depends on definitions:  df-bi 210  df-an 400  df-or 845  df-3an 1086  df-tru 1541  df-ex 1782  df-nf 1786  df-sb 2071  df-mo 2624  df-eu 2655  df-clab 2803  df-cleq 2817  df-clel 2896  df-nfc 2964  df-ne 3015  df-ral 3138  df-rex 3139  df-rab 3142  df-v 3482  df-sbc 3759  df-dif 3922  df-un 3924  df-in 3926  df-ss 3936  df-nul 4277  df-if 4451  df-sn 4551  df-pr 4553  df-op 4557  df-uni 4825  df-br 5053  df-opab 5115  df-mpt 5133  df-id 5447  df-xp 5548  df-rel 5549  df-cnv 5550  df-co 5551  df-dm 5552  df-iota 6302  df-fun 6345  df-fv 6351  df-ov 7152  df-0g 16715  df-mnd 17912 This theorem is referenced by: (None)
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