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Theorem dfgrp2 18847
Description: Alternate definition of a group as semigroup with a left identity and a left inverse for each element. This "definition" is weaker than df-grp 18822, based on the definition of a monoid which provides a left and a right identity. (Contributed by AV, 28-Aug-2021.)
Hypotheses
Ref Expression
dfgrp2.b 𝐵 = (Base‘𝐺)
dfgrp2.p + = (+g𝐺)
Assertion
Ref Expression
dfgrp2 (𝐺 ∈ Grp ↔ (𝐺 ∈ Smgrp ∧ ∃𝑛𝐵𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)))
Distinct variable groups:   𝐵,𝑖,𝑛,𝑥   𝑖,𝐺,𝑛,𝑥   + ,𝑖,𝑛,𝑥

Proof of Theorem dfgrp2
Dummy variables 𝑎 𝑏 𝑐 are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 grpsgrp 18846 . . 3 (𝐺 ∈ Grp → 𝐺 ∈ Smgrp)
2 grpmnd 18826 . . . . 5 (𝐺 ∈ Grp → 𝐺 ∈ Mnd)
3 dfgrp2.b . . . . . 6 𝐵 = (Base‘𝐺)
4 eqid 2733 . . . . . 6 (0g𝐺) = (0g𝐺)
53, 4mndidcl 18640 . . . . 5 (𝐺 ∈ Mnd → (0g𝐺) ∈ 𝐵)
62, 5syl 17 . . . 4 (𝐺 ∈ Grp → (0g𝐺) ∈ 𝐵)
7 oveq1 7416 . . . . . . . 8 (𝑛 = (0g𝐺) → (𝑛 + 𝑥) = ((0g𝐺) + 𝑥))
87eqeq1d 2735 . . . . . . 7 (𝑛 = (0g𝐺) → ((𝑛 + 𝑥) = 𝑥 ↔ ((0g𝐺) + 𝑥) = 𝑥))
9 eqeq2 2745 . . . . . . . 8 (𝑛 = (0g𝐺) → ((𝑖 + 𝑥) = 𝑛 ↔ (𝑖 + 𝑥) = (0g𝐺)))
109rexbidv 3179 . . . . . . 7 (𝑛 = (0g𝐺) → (∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛 ↔ ∃𝑖𝐵 (𝑖 + 𝑥) = (0g𝐺)))
118, 10anbi12d 632 . . . . . 6 (𝑛 = (0g𝐺) → (((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛) ↔ (((0g𝐺) + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = (0g𝐺))))
1211ralbidv 3178 . . . . 5 (𝑛 = (0g𝐺) → (∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛) ↔ ∀𝑥𝐵 (((0g𝐺) + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = (0g𝐺))))
1312adantl 483 . . . 4 ((𝐺 ∈ Grp ∧ 𝑛 = (0g𝐺)) → (∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛) ↔ ∀𝑥𝐵 (((0g𝐺) + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = (0g𝐺))))
14 dfgrp2.p . . . . . . . 8 + = (+g𝐺)
153, 14, 4mndlid 18645 . . . . . . 7 ((𝐺 ∈ Mnd ∧ 𝑥𝐵) → ((0g𝐺) + 𝑥) = 𝑥)
162, 15sylan 581 . . . . . 6 ((𝐺 ∈ Grp ∧ 𝑥𝐵) → ((0g𝐺) + 𝑥) = 𝑥)
173, 14, 4grpinvex 18829 . . . . . 6 ((𝐺 ∈ Grp ∧ 𝑥𝐵) → ∃𝑖𝐵 (𝑖 + 𝑥) = (0g𝐺))
1816, 17jca 513 . . . . 5 ((𝐺 ∈ Grp ∧ 𝑥𝐵) → (((0g𝐺) + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = (0g𝐺)))
1918ralrimiva 3147 . . . 4 (𝐺 ∈ Grp → ∀𝑥𝐵 (((0g𝐺) + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = (0g𝐺)))
206, 13, 19rspcedvd 3615 . . 3 (𝐺 ∈ Grp → ∃𝑛𝐵𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛))
211, 20jca 513 . 2 (𝐺 ∈ Grp → (𝐺 ∈ Smgrp ∧ ∃𝑛𝐵𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)))
223a1i 11 . . . . . 6 (((𝑛𝐵 ∧ ∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)) ∧ 𝐺 ∈ Smgrp) → 𝐵 = (Base‘𝐺))
2314a1i 11 . . . . . 6 (((𝑛𝐵 ∧ ∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)) ∧ 𝐺 ∈ Smgrp) → + = (+g𝐺))
24 sgrpmgm 18615 . . . . . . . 8 (𝐺 ∈ Smgrp → 𝐺 ∈ Mgm)
2524adantl 483 . . . . . . 7 (((𝑛𝐵 ∧ ∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)) ∧ 𝐺 ∈ Smgrp) → 𝐺 ∈ Mgm)
263, 14mgmcl 18564 . . . . . . 7 ((𝐺 ∈ Mgm ∧ 𝑎𝐵𝑏𝐵) → (𝑎 + 𝑏) ∈ 𝐵)
2725, 26syl3an1 1164 . . . . . 6 ((((𝑛𝐵 ∧ ∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)) ∧ 𝐺 ∈ Smgrp) ∧ 𝑎𝐵𝑏𝐵) → (𝑎 + 𝑏) ∈ 𝐵)
283, 14sgrpass 18616 . . . . . . 7 ((𝐺 ∈ Smgrp ∧ (𝑎𝐵𝑏𝐵𝑐𝐵)) → ((𝑎 + 𝑏) + 𝑐) = (𝑎 + (𝑏 + 𝑐)))
2928adantll 713 . . . . . 6 ((((𝑛𝐵 ∧ ∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)) ∧ 𝐺 ∈ Smgrp) ∧ (𝑎𝐵𝑏𝐵𝑐𝐵)) → ((𝑎 + 𝑏) + 𝑐) = (𝑎 + (𝑏 + 𝑐)))
30 simpll 766 . . . . . 6 (((𝑛𝐵 ∧ ∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)) ∧ 𝐺 ∈ Smgrp) → 𝑛𝐵)
31 oveq2 7417 . . . . . . . . . . . 12 (𝑥 = 𝑎 → (𝑛 + 𝑥) = (𝑛 + 𝑎))
32 id 22 . . . . . . . . . . . 12 (𝑥 = 𝑎𝑥 = 𝑎)
3331, 32eqeq12d 2749 . . . . . . . . . . 11 (𝑥 = 𝑎 → ((𝑛 + 𝑥) = 𝑥 ↔ (𝑛 + 𝑎) = 𝑎))
34 oveq2 7417 . . . . . . . . . . . . 13 (𝑥 = 𝑎 → (𝑖 + 𝑥) = (𝑖 + 𝑎))
3534eqeq1d 2735 . . . . . . . . . . . 12 (𝑥 = 𝑎 → ((𝑖 + 𝑥) = 𝑛 ↔ (𝑖 + 𝑎) = 𝑛))
3635rexbidv 3179 . . . . . . . . . . 11 (𝑥 = 𝑎 → (∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛 ↔ ∃𝑖𝐵 (𝑖 + 𝑎) = 𝑛))
3733, 36anbi12d 632 . . . . . . . . . 10 (𝑥 = 𝑎 → (((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛) ↔ ((𝑛 + 𝑎) = 𝑎 ∧ ∃𝑖𝐵 (𝑖 + 𝑎) = 𝑛)))
3837rspcv 3609 . . . . . . . . 9 (𝑎𝐵 → (∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛) → ((𝑛 + 𝑎) = 𝑎 ∧ ∃𝑖𝐵 (𝑖 + 𝑎) = 𝑛)))
39 simpl 484 . . . . . . . . 9 (((𝑛 + 𝑎) = 𝑎 ∧ ∃𝑖𝐵 (𝑖 + 𝑎) = 𝑛) → (𝑛 + 𝑎) = 𝑎)
4038, 39syl6com 37 . . . . . . . 8 (∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛) → (𝑎𝐵 → (𝑛 + 𝑎) = 𝑎))
4140ad2antlr 726 . . . . . . 7 (((𝑛𝐵 ∧ ∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)) ∧ 𝐺 ∈ Smgrp) → (𝑎𝐵 → (𝑛 + 𝑎) = 𝑎))
4241imp 408 . . . . . 6 ((((𝑛𝐵 ∧ ∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)) ∧ 𝐺 ∈ Smgrp) ∧ 𝑎𝐵) → (𝑛 + 𝑎) = 𝑎)
43 oveq1 7416 . . . . . . . . . . . . 13 (𝑖 = 𝑏 → (𝑖 + 𝑎) = (𝑏 + 𝑎))
4443eqeq1d 2735 . . . . . . . . . . . 12 (𝑖 = 𝑏 → ((𝑖 + 𝑎) = 𝑛 ↔ (𝑏 + 𝑎) = 𝑛))
4544cbvrexvw 3236 . . . . . . . . . . 11 (∃𝑖𝐵 (𝑖 + 𝑎) = 𝑛 ↔ ∃𝑏𝐵 (𝑏 + 𝑎) = 𝑛)
4645biimpi 215 . . . . . . . . . 10 (∃𝑖𝐵 (𝑖 + 𝑎) = 𝑛 → ∃𝑏𝐵 (𝑏 + 𝑎) = 𝑛)
4746adantl 483 . . . . . . . . 9 (((𝑛 + 𝑎) = 𝑎 ∧ ∃𝑖𝐵 (𝑖 + 𝑎) = 𝑛) → ∃𝑏𝐵 (𝑏 + 𝑎) = 𝑛)
4838, 47syl6com 37 . . . . . . . 8 (∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛) → (𝑎𝐵 → ∃𝑏𝐵 (𝑏 + 𝑎) = 𝑛))
4948ad2antlr 726 . . . . . . 7 (((𝑛𝐵 ∧ ∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)) ∧ 𝐺 ∈ Smgrp) → (𝑎𝐵 → ∃𝑏𝐵 (𝑏 + 𝑎) = 𝑛))
5049imp 408 . . . . . 6 ((((𝑛𝐵 ∧ ∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)) ∧ 𝐺 ∈ Smgrp) ∧ 𝑎𝐵) → ∃𝑏𝐵 (𝑏 + 𝑎) = 𝑛)
5122, 23, 27, 29, 30, 42, 50isgrpde 18843 . . . . 5 (((𝑛𝐵 ∧ ∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)) ∧ 𝐺 ∈ Smgrp) → 𝐺 ∈ Grp)
5251ex 414 . . . 4 ((𝑛𝐵 ∧ ∀𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)) → (𝐺 ∈ Smgrp → 𝐺 ∈ Grp))
5352rexlimiva 3148 . . 3 (∃𝑛𝐵𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛) → (𝐺 ∈ Smgrp → 𝐺 ∈ Grp))
5453impcom 409 . 2 ((𝐺 ∈ Smgrp ∧ ∃𝑛𝐵𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)) → 𝐺 ∈ Grp)
5521, 54impbii 208 1 (𝐺 ∈ Grp ↔ (𝐺 ∈ Smgrp ∧ ∃𝑛𝐵𝑥𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖𝐵 (𝑖 + 𝑥) = 𝑛)))
Colors of variables: wff setvar class
Syntax hints:  wi 4  wb 205  wa 397  w3a 1088   = wceq 1542  wcel 2107  wral 3062  wrex 3071  cfv 6544  (class class class)co 7409  Basecbs 17144  +gcplusg 17197  0gc0g 17385  Mgmcmgm 18559  Smgrpcsgrp 18609  Mndcmnd 18625  Grpcgrp 18819
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1798  ax-4 1812  ax-5 1914  ax-6 1972  ax-7 2012  ax-8 2109  ax-9 2117  ax-10 2138  ax-11 2155  ax-12 2172  ax-ext 2704  ax-sep 5300  ax-nul 5307  ax-pr 5428
This theorem depends on definitions:  df-bi 206  df-an 398  df-or 847  df-3an 1090  df-tru 1545  df-fal 1555  df-ex 1783  df-nf 1787  df-sb 2069  df-mo 2535  df-eu 2564  df-clab 2711  df-cleq 2725  df-clel 2811  df-nfc 2886  df-ne 2942  df-ral 3063  df-rex 3072  df-rmo 3377  df-reu 3378  df-rab 3434  df-v 3477  df-sbc 3779  df-dif 3952  df-un 3954  df-in 3956  df-ss 3966  df-nul 4324  df-if 4530  df-sn 4630  df-pr 4632  df-op 4636  df-uni 4910  df-br 5150  df-opab 5212  df-mpt 5233  df-id 5575  df-xp 5683  df-rel 5684  df-cnv 5685  df-co 5686  df-dm 5687  df-iota 6496  df-fun 6546  df-fv 6552  df-riota 7365  df-ov 7412  df-0g 17387  df-mgm 18561  df-sgrp 18610  df-mnd 18626  df-grp 18822
This theorem is referenced by:  dfgrp2e  18848  dfgrp3  18922
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