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| Type | Label | Description |
|---|---|---|
| Statement | ||
| Theorem | efmndid 18901 | The identity function restricted to a set 𝐴 is the identity element of the monoid of endofunctions on 𝐴. (Contributed by AV, 25-Jan-2024.) |
| ⊢ 𝐺 = (EndoFMnd‘𝐴) ⇒ ⊢ (𝐴 ∈ 𝑉 → ( I ↾ 𝐴) = (0g‘𝐺)) | ||
| Theorem | efmndmnd 18902 | The monoid of endofunctions on a set 𝐴 is actually a monoid. (Contributed by AV, 31-Jan-2024.) |
| ⊢ 𝐺 = (EndoFMnd‘𝐴) ⇒ ⊢ (𝐴 ∈ 𝑉 → 𝐺 ∈ Mnd) | ||
| Theorem | efmnd0nmnd 18903 | Even the monoid of endofunctions on the empty set is actually a monoid. (Contributed by AV, 31-Jan-2024.) |
| ⊢ (EndoFMnd‘∅) ∈ Mnd | ||
| Theorem | efmndbas0 18904 | The base set of the monoid of endofunctions on the empty set is the singleton containing the empty set. (Contributed by AV, 27-Jan-2024.) (Proof shortened by AV, 31-Mar-2024.) |
| ⊢ (Base‘(EndoFMnd‘∅)) = {∅} | ||
| Theorem | efmnd1hash 18905 | The monoid of endofunctions on a singleton has cardinality 1. (Contributed by AV, 27-Jan-2024.) |
| ⊢ 𝐺 = (EndoFMnd‘𝐴) & ⊢ 𝐵 = (Base‘𝐺) & ⊢ 𝐴 = {𝐼} ⇒ ⊢ (𝐼 ∈ 𝑉 → (♯‘𝐵) = 1) | ||
| Theorem | efmnd1bas 18906 | The monoid of endofunctions on a singleton consists of the identity only. (Contributed by AV, 31-Jan-2024.) |
| ⊢ 𝐺 = (EndoFMnd‘𝐴) & ⊢ 𝐵 = (Base‘𝐺) & ⊢ 𝐴 = {𝐼} ⇒ ⊢ (𝐼 ∈ 𝑉 → 𝐵 = {{〈𝐼, 𝐼〉}}) | ||
| Theorem | efmnd2hash 18907 | The monoid of endofunctions on a (proper) pair has cardinality 4. (Contributed by AV, 18-Feb-2024.) |
| ⊢ 𝐺 = (EndoFMnd‘𝐴) & ⊢ 𝐵 = (Base‘𝐺) & ⊢ 𝐴 = {𝐼, 𝐽} ⇒ ⊢ ((𝐼 ∈ 𝑉 ∧ 𝐽 ∈ 𝑊 ∧ 𝐼 ≠ 𝐽) → (♯‘𝐵) = 4) | ||
| Theorem | submefmnd 18908* | If the base set of a monoid is contained in the base set of the monoid of endofunctions on a set 𝐴, contains the identity function and has the function composition as group operation, then its base set is a submonoid of the monoid of endofunctions on set 𝐴. Analogous to pgrpsubgsymg 19427. (Contributed by AV, 17-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘𝐴) & ⊢ 𝐵 = (Base‘𝑀) & ⊢ 0 = (0g‘𝑀) & ⊢ 𝐹 = (Base‘𝑆) ⇒ ⊢ (𝐴 ∈ 𝑉 → (((𝑆 ∈ Mnd ∧ 𝐹 ⊆ 𝐵 ∧ 0 ∈ 𝐹) ∧ (+g‘𝑆) = (𝑓 ∈ 𝐹, 𝑔 ∈ 𝐹 ↦ (𝑓 ∘ 𝑔))) → 𝐹 ∈ (SubMnd‘𝑀))) | ||
| Theorem | sursubmefmnd 18909* | The set of surjective endofunctions on a set 𝐴 is a submonoid of the monoid of endofunctions on 𝐴. (Contributed by AV, 25-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘𝐴) ⇒ ⊢ (𝐴 ∈ 𝑉 → {ℎ ∣ ℎ:𝐴–onto→𝐴} ∈ (SubMnd‘𝑀)) | ||
| Theorem | injsubmefmnd 18910* | The set of injective endofunctions on a set 𝐴 is a submonoid of the monoid of endofunctions on 𝐴. (Contributed by AV, 25-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘𝐴) ⇒ ⊢ (𝐴 ∈ 𝑉 → {ℎ ∣ ℎ:𝐴–1-1→𝐴} ∈ (SubMnd‘𝑀)) | ||
| Theorem | idressubmefmnd 18911 | The singleton containing only the identity function restricted to a set is a submonoid of the monoid of endofunctions on this set. (Contributed by AV, 17-Feb-2024.) |
| ⊢ 𝐺 = (EndoFMnd‘𝐴) ⇒ ⊢ (𝐴 ∈ 𝑉 → {( I ↾ 𝐴)} ∈ (SubMnd‘𝐺)) | ||
| Theorem | idresefmnd 18912 | The structure with the singleton containing only the identity function restricted to a set 𝐴 as base set and the function composition as group operation, constructed by (structure) restricting the monoid of endofunctions on 𝐴 to that singleton, is a monoid whose base set is a subset of the base set of the monoid of endofunctions on 𝐴. (Contributed by AV, 17-Feb-2024.) |
| ⊢ 𝐺 = (EndoFMnd‘𝐴) & ⊢ 𝐸 = (𝐺 ↾s {( I ↾ 𝐴)}) ⇒ ⊢ (𝐴 ∈ 𝑉 → (𝐸 ∈ Mnd ∧ (Base‘𝐸) ⊆ (Base‘𝐺))) | ||
| Theorem | smndex1ibas 18913 | The modulo function 𝐼 is an endofunction on ℕ0. (Contributed by AV, 12-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) ⇒ ⊢ 𝐼 ∈ (Base‘𝑀) | ||
| Theorem | smndex1iidm 18914* | The modulo function 𝐼 is idempotent. (Contributed by AV, 12-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) ⇒ ⊢ (𝐼 ∘ 𝐼) = 𝐼 | ||
| Theorem | smndex1gbas 18915* | The constant functions (𝐺‘𝐾) are endofunctions on ℕ0. (Contributed by AV, 12-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) & ⊢ 𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛)) ⇒ ⊢ (𝐾 ∈ (0..^𝑁) → (𝐺‘𝐾) ∈ (Base‘𝑀)) | ||
| Theorem | smndex1gid 18916* | The composition of a constant function (𝐺‘𝐾) with another endofunction on ℕ0 results in (𝐺‘𝐾) itself. (Contributed by AV, 14-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) & ⊢ 𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛)) ⇒ ⊢ ((𝐹 ∈ (Base‘𝑀) ∧ 𝐾 ∈ (0..^𝑁)) → ((𝐺‘𝐾) ∘ 𝐹) = (𝐺‘𝐾)) | ||
| Theorem | smndex1igid 18917* | The composition of the modulo function 𝐼 and a constant function (𝐺‘𝐾) results in (𝐺‘𝐾) itself. (Contributed by AV, 14-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) & ⊢ 𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛)) ⇒ ⊢ (𝐾 ∈ (0..^𝑁) → (𝐼 ∘ (𝐺‘𝐾)) = (𝐺‘𝐾)) | ||
| Theorem | smndex1basss 18918* | The modulo function 𝐼 and the constant functions (𝐺‘𝐾) are endofunctions on ℕ0. (Contributed by AV, 12-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) & ⊢ 𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛)) & ⊢ 𝐵 = ({𝐼} ∪ ∪ 𝑛 ∈ (0..^𝑁){(𝐺‘𝑛)}) ⇒ ⊢ 𝐵 ⊆ (Base‘𝑀) | ||
| Theorem | smndex1bas 18919* | The base set of the monoid of endofunctions on ℕ0 restricted to the modulo function 𝐼 and the constant functions (𝐺‘𝐾). (Contributed by AV, 12-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) & ⊢ 𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛)) & ⊢ 𝐵 = ({𝐼} ∪ ∪ 𝑛 ∈ (0..^𝑁){(𝐺‘𝑛)}) & ⊢ 𝑆 = (𝑀 ↾s 𝐵) ⇒ ⊢ (Base‘𝑆) = 𝐵 | ||
| Theorem | smndex1mgm 18920* | The monoid of endofunctions on ℕ0 restricted to the modulo function 𝐼 and the constant functions (𝐺‘𝐾) is a magma. (Contributed by AV, 14-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) & ⊢ 𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛)) & ⊢ 𝐵 = ({𝐼} ∪ ∪ 𝑛 ∈ (0..^𝑁){(𝐺‘𝑛)}) & ⊢ 𝑆 = (𝑀 ↾s 𝐵) ⇒ ⊢ 𝑆 ∈ Mgm | ||
| Theorem | smndex1sgrp 18921* | The monoid of endofunctions on ℕ0 restricted to the modulo function 𝐼 and the constant functions (𝐺‘𝐾) is a semigroup. (Contributed by AV, 14-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) & ⊢ 𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛)) & ⊢ 𝐵 = ({𝐼} ∪ ∪ 𝑛 ∈ (0..^𝑁){(𝐺‘𝑛)}) & ⊢ 𝑆 = (𝑀 ↾s 𝐵) ⇒ ⊢ 𝑆 ∈ Smgrp | ||
| Theorem | smndex1mndlem 18922* | Lemma for smndex1mnd 18923 and smndex1id 18924. (Contributed by AV, 16-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) & ⊢ 𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛)) & ⊢ 𝐵 = ({𝐼} ∪ ∪ 𝑛 ∈ (0..^𝑁){(𝐺‘𝑛)}) & ⊢ 𝑆 = (𝑀 ↾s 𝐵) ⇒ ⊢ (𝑋 ∈ 𝐵 → ((𝐼 ∘ 𝑋) = 𝑋 ∧ (𝑋 ∘ 𝐼) = 𝑋)) | ||
| Theorem | smndex1mnd 18923* | The monoid of endofunctions on ℕ0 restricted to the modulo function 𝐼 and the constant functions (𝐺‘𝐾) is a monoid. (Contributed by AV, 16-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) & ⊢ 𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛)) & ⊢ 𝐵 = ({𝐼} ∪ ∪ 𝑛 ∈ (0..^𝑁){(𝐺‘𝑛)}) & ⊢ 𝑆 = (𝑀 ↾s 𝐵) ⇒ ⊢ 𝑆 ∈ Mnd | ||
| Theorem | smndex1id 18924* | The modulo function 𝐼 is the identity of the monoid of endofunctions on ℕ0 restricted to the modulo function 𝐼 and the constant functions (𝐺‘𝐾). (Contributed by AV, 16-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) & ⊢ 𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛)) & ⊢ 𝐵 = ({𝐼} ∪ ∪ 𝑛 ∈ (0..^𝑁){(𝐺‘𝑛)}) & ⊢ 𝑆 = (𝑀 ↾s 𝐵) ⇒ ⊢ 𝐼 = (0g‘𝑆) | ||
| Theorem | smndex1n0mnd 18925* | The identity of the monoid 𝑀 of endofunctions on set ℕ0 is not contained in the base set of the constructed monoid 𝑆. (Contributed by AV, 17-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) & ⊢ 𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛)) & ⊢ 𝐵 = ({𝐼} ∪ ∪ 𝑛 ∈ (0..^𝑁){(𝐺‘𝑛)}) & ⊢ 𝑆 = (𝑀 ↾s 𝐵) ⇒ ⊢ (0g‘𝑀) ∉ 𝐵 | ||
| Theorem | nsmndex1 18926* | The base set 𝐵 of the constructed monoid 𝑆 is not a submonoid of the monoid 𝑀 of endofunctions on set ℕ0, although 𝑀 ∈ Mnd and 𝑆 ∈ Mnd and 𝐵 ⊆ (Base‘𝑀) hold. (Contributed by AV, 17-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝑁 ∈ ℕ & ⊢ 𝐼 = (𝑥 ∈ ℕ0 ↦ (𝑥 mod 𝑁)) & ⊢ 𝐺 = (𝑛 ∈ (0..^𝑁) ↦ (𝑥 ∈ ℕ0 ↦ 𝑛)) & ⊢ 𝐵 = ({𝐼} ∪ ∪ 𝑛 ∈ (0..^𝑁){(𝐺‘𝑛)}) & ⊢ 𝑆 = (𝑀 ↾s 𝐵) ⇒ ⊢ 𝐵 ∉ (SubMnd‘𝑀) | ||
| Theorem | smndex2dbas 18927 | The doubling function 𝐷 is an endofunction on ℕ0. (Contributed by AV, 18-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝐵 = (Base‘𝑀) & ⊢ 0 = (0g‘𝑀) & ⊢ 𝐷 = (𝑥 ∈ ℕ0 ↦ (2 · 𝑥)) ⇒ ⊢ 𝐷 ∈ 𝐵 | ||
| Theorem | smndex2dnrinv 18928 | The doubling function 𝐷 has no right inverse in the monoid of endofunctions on ℕ0. (Contributed by AV, 18-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝐵 = (Base‘𝑀) & ⊢ 0 = (0g‘𝑀) & ⊢ 𝐷 = (𝑥 ∈ ℕ0 ↦ (2 · 𝑥)) ⇒ ⊢ ∀𝑓 ∈ 𝐵 (𝐷 ∘ 𝑓) ≠ 0 | ||
| Theorem | smndex2hbas 18929 | The halving functions 𝐻 are endofunctions on ℕ0. (Contributed by AV, 18-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝐵 = (Base‘𝑀) & ⊢ 0 = (0g‘𝑀) & ⊢ 𝐷 = (𝑥 ∈ ℕ0 ↦ (2 · 𝑥)) & ⊢ 𝑁 ∈ ℕ0 & ⊢ 𝐻 = (𝑥 ∈ ℕ0 ↦ if(2 ∥ 𝑥, (𝑥 / 2), 𝑁)) ⇒ ⊢ 𝐻 ∈ 𝐵 | ||
| Theorem | smndex2dlinvh 18930* | The halving functions 𝐻 are left inverses of the doubling function 𝐷. (Contributed by AV, 18-Feb-2024.) |
| ⊢ 𝑀 = (EndoFMnd‘ℕ0) & ⊢ 𝐵 = (Base‘𝑀) & ⊢ 0 = (0g‘𝑀) & ⊢ 𝐷 = (𝑥 ∈ ℕ0 ↦ (2 · 𝑥)) & ⊢ 𝑁 ∈ ℕ0 & ⊢ 𝐻 = (𝑥 ∈ ℕ0 ↦ if(2 ∥ 𝑥, (𝑥 / 2), 𝑁)) ⇒ ⊢ (𝐻 ∘ 𝐷) = 0 | ||
| Theorem | mgm2nsgrplem1 18931* | Lemma 1 for mgm2nsgrp 18935: 𝑀 is a magma, even if 𝐴 = 𝐵 (𝑀 is the trivial magma in this case, see mgmb1mgm1 18668). (Contributed by AV, 27-Jan-2020.) |
| ⊢ 𝑆 = {𝐴, 𝐵} & ⊢ (Base‘𝑀) = 𝑆 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ if((𝑥 = 𝐴 ∧ 𝑦 = 𝐴), 𝐵, 𝐴)) ⇒ ⊢ ((𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑊) → 𝑀 ∈ Mgm) | ||
| Theorem | mgm2nsgrplem2 18932* | Lemma 2 for mgm2nsgrp 18935. (Contributed by AV, 27-Jan-2020.) |
| ⊢ 𝑆 = {𝐴, 𝐵} & ⊢ (Base‘𝑀) = 𝑆 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ if((𝑥 = 𝐴 ∧ 𝑦 = 𝐴), 𝐵, 𝐴)) & ⊢ ⚬ = (+g‘𝑀) ⇒ ⊢ ((𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑊) → ((𝐴 ⚬ 𝐴) ⚬ 𝐵) = 𝐴) | ||
| Theorem | mgm2nsgrplem3 18933* | Lemma 3 for mgm2nsgrp 18935. (Contributed by AV, 28-Jan-2020.) |
| ⊢ 𝑆 = {𝐴, 𝐵} & ⊢ (Base‘𝑀) = 𝑆 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ if((𝑥 = 𝐴 ∧ 𝑦 = 𝐴), 𝐵, 𝐴)) & ⊢ ⚬ = (+g‘𝑀) ⇒ ⊢ ((𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑊) → (𝐴 ⚬ (𝐴 ⚬ 𝐵)) = 𝐵) | ||
| Theorem | mgm2nsgrplem4 18934* | Lemma 4 for mgm2nsgrp 18935: M is not a semigroup. (Contributed by AV, 28-Jan-2020.) (Proof shortened by AV, 31-Jan-2020.) |
| ⊢ 𝑆 = {𝐴, 𝐵} & ⊢ (Base‘𝑀) = 𝑆 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ if((𝑥 = 𝐴 ∧ 𝑦 = 𝐴), 𝐵, 𝐴)) ⇒ ⊢ ((♯‘𝑆) = 2 → 𝑀 ∉ Smgrp) | ||
| Theorem | mgm2nsgrp 18935* | A small magma (with two elements) which is not a semigroup. (Contributed by AV, 28-Jan-2020.) |
| ⊢ 𝑆 = {𝐴, 𝐵} & ⊢ (Base‘𝑀) = 𝑆 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ if((𝑥 = 𝐴 ∧ 𝑦 = 𝐴), 𝐵, 𝐴)) ⇒ ⊢ ((♯‘𝑆) = 2 → (𝑀 ∈ Mgm ∧ 𝑀 ∉ Smgrp)) | ||
| Theorem | sgrp2nmndlem1 18936* | Lemma 1 for sgrp2nmnd 18943: 𝑀 is a magma, even if 𝐴 = 𝐵 (𝑀 is the trivial magma in this case, see mgmb1mgm1 18668). (Contributed by AV, 29-Jan-2020.) |
| ⊢ 𝑆 = {𝐴, 𝐵} & ⊢ (Base‘𝑀) = 𝑆 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ if(𝑥 = 𝐴, 𝐴, 𝐵)) ⇒ ⊢ ((𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑊) → 𝑀 ∈ Mgm) | ||
| Theorem | sgrp2nmndlem2 18937* | Lemma 2 for sgrp2nmnd 18943. (Contributed by AV, 29-Jan-2020.) |
| ⊢ 𝑆 = {𝐴, 𝐵} & ⊢ (Base‘𝑀) = 𝑆 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ if(𝑥 = 𝐴, 𝐴, 𝐵)) & ⊢ ⚬ = (+g‘𝑀) ⇒ ⊢ ((𝐴 ∈ 𝑆 ∧ 𝐶 ∈ 𝑆) → (𝐴 ⚬ 𝐶) = 𝐴) | ||
| Theorem | sgrp2nmndlem3 18938* | Lemma 3 for sgrp2nmnd 18943. (Contributed by AV, 29-Jan-2020.) |
| ⊢ 𝑆 = {𝐴, 𝐵} & ⊢ (Base‘𝑀) = 𝑆 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ if(𝑥 = 𝐴, 𝐴, 𝐵)) & ⊢ ⚬ = (+g‘𝑀) ⇒ ⊢ ((𝐶 ∈ 𝑆 ∧ 𝐵 ∈ 𝑆 ∧ 𝐴 ≠ 𝐵) → (𝐵 ⚬ 𝐶) = 𝐵) | ||
| Theorem | sgrp2rid2 18939* | A small semigroup (with two elements) with two right identities which are different if 𝐴 ≠ 𝐵. (Contributed by AV, 10-Feb-2020.) |
| ⊢ 𝑆 = {𝐴, 𝐵} & ⊢ (Base‘𝑀) = 𝑆 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ if(𝑥 = 𝐴, 𝐴, 𝐵)) & ⊢ ⚬ = (+g‘𝑀) ⇒ ⊢ ((𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑊) → ∀𝑥 ∈ 𝑆 ∀𝑦 ∈ 𝑆 (𝑦 ⚬ 𝑥) = 𝑦) | ||
| Theorem | sgrp2rid2ex 18940* | A small semigroup (with two elements) with two right identities which are different. (Contributed by AV, 10-Feb-2020.) |
| ⊢ 𝑆 = {𝐴, 𝐵} & ⊢ (Base‘𝑀) = 𝑆 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ if(𝑥 = 𝐴, 𝐴, 𝐵)) & ⊢ ⚬ = (+g‘𝑀) ⇒ ⊢ ((♯‘𝑆) = 2 → ∃𝑥 ∈ 𝑆 ∃𝑧 ∈ 𝑆 ∀𝑦 ∈ 𝑆 (𝑥 ≠ 𝑧 ∧ (𝑦 ⚬ 𝑥) = 𝑦 ∧ (𝑦 ⚬ 𝑧) = 𝑦)) | ||
| Theorem | sgrp2nmndlem4 18941* | Lemma 4 for sgrp2nmnd 18943: M is a semigroup. (Contributed by AV, 29-Jan-2020.) |
| ⊢ 𝑆 = {𝐴, 𝐵} & ⊢ (Base‘𝑀) = 𝑆 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ if(𝑥 = 𝐴, 𝐴, 𝐵)) ⇒ ⊢ ((♯‘𝑆) = 2 → 𝑀 ∈ Smgrp) | ||
| Theorem | sgrp2nmndlem5 18942* | Lemma 5 for sgrp2nmnd 18943: M is not a monoid. (Contributed by AV, 29-Jan-2020.) |
| ⊢ 𝑆 = {𝐴, 𝐵} & ⊢ (Base‘𝑀) = 𝑆 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ if(𝑥 = 𝐴, 𝐴, 𝐵)) ⇒ ⊢ ((♯‘𝑆) = 2 → 𝑀 ∉ Mnd) | ||
| Theorem | sgrp2nmnd 18943* | A small semigroup (with two elements) which is not a monoid. (Contributed by AV, 26-Jan-2020.) |
| ⊢ 𝑆 = {𝐴, 𝐵} & ⊢ (Base‘𝑀) = 𝑆 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝑆, 𝑦 ∈ 𝑆 ↦ if(𝑥 = 𝐴, 𝐴, 𝐵)) ⇒ ⊢ ((♯‘𝑆) = 2 → (𝑀 ∈ Smgrp ∧ 𝑀 ∉ Mnd)) | ||
| Theorem | mgmnsgrpex 18944 | There is a magma which is not a semigroup. (Contributed by AV, 29-Jan-2020.) |
| ⊢ ∃𝑚 ∈ Mgm 𝑚 ∉ Smgrp | ||
| Theorem | sgrpnmndex 18945 | There is a semigroup which is not a monoid. (Contributed by AV, 29-Jan-2020.) |
| ⊢ ∃𝑚 ∈ Smgrp 𝑚 ∉ Mnd | ||
| Theorem | sgrpssmgm 18946 | The class of all semigroups is a proper subclass of the class of all magmas. (Contributed by AV, 29-Jan-2020.) |
| ⊢ Smgrp ⊊ Mgm | ||
| Theorem | mndsssgrp 18947 | The class of all monoids is a proper subclass of the class of all semigroups. (Contributed by AV, 29-Jan-2020.) |
| ⊢ Mnd ⊊ Smgrp | ||
| Theorem | pwmndgplus 18948* | The operation of the monoid of the power set of a class 𝐴 under union. (Contributed by AV, 27-Feb-2024.) |
| ⊢ (Base‘𝑀) = 𝒫 𝐴 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝒫 𝐴, 𝑦 ∈ 𝒫 𝐴 ↦ (𝑥 ∪ 𝑦)) ⇒ ⊢ ((𝑋 ∈ 𝒫 𝐴 ∧ 𝑌 ∈ 𝒫 𝐴) → (𝑋(+g‘𝑀)𝑌) = (𝑋 ∪ 𝑌)) | ||
| Theorem | pwmndid 18949* | The identity of the monoid of the power set of a class 𝐴 under union is the empty set. (Contributed by AV, 27-Feb-2024.) |
| ⊢ (Base‘𝑀) = 𝒫 𝐴 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝒫 𝐴, 𝑦 ∈ 𝒫 𝐴 ↦ (𝑥 ∪ 𝑦)) ⇒ ⊢ (0g‘𝑀) = ∅ | ||
| Theorem | pwmnd 18950* | The power set of a class 𝐴 is a monoid under union. (Contributed by AV, 27-Feb-2024.) |
| ⊢ (Base‘𝑀) = 𝒫 𝐴 & ⊢ (+g‘𝑀) = (𝑥 ∈ 𝒫 𝐴, 𝑦 ∈ 𝒫 𝐴 ↦ (𝑥 ∪ 𝑦)) ⇒ ⊢ 𝑀 ∈ Mnd | ||
| Syntax | cgrp 18951 | Extend class notation with class of all groups. |
| class Grp | ||
| Syntax | cminusg 18952 | Extend class notation with inverse of group element. |
| class invg | ||
| Syntax | csg 18953 | Extend class notation with group subtraction (or division) operation. |
| class -g | ||
| Definition | df-grp 18954* | Define class of all groups. A group is a monoid (df-mnd 18748) whose internal operation is such that every element admits a left inverse (which can be proven to be a two-sided inverse). Thus, a group 𝐺 is an algebraic structure formed from a base set of elements (notated (Base‘𝐺) per df-base 17248) and an internal group operation (notated (+g‘𝐺) per df-plusg 17310). The operation combines any two elements of the group base set and must satisfy the 4 group axioms: closure (the result of the group operation must always be a member of the base set, see grpcl 18959), associativity (so ((𝑎+g𝑏)+g𝑐) = (𝑎+g(𝑏+g𝑐)) for any a, b, c, see grpass 18960), identity (there must be an element 𝑒 = (0g‘𝐺) such that 𝑒+g𝑎 = 𝑎+g𝑒 = 𝑎 for any a), and inverse (for each element a in the base set, there must be an element 𝑏 = invg𝑎 in the base set such that 𝑎+g𝑏 = 𝑏+g𝑎 = 𝑒). It can be proven that the identity element is unique (grpideu 18962). Groups need not be commutative; a commutative group is an Abelian group (see df-abl 19801). Subgroups can often be formed from groups, see df-subg 19141. An example of an (Abelian) group is the set of complex numbers ℂ over the group operation + (addition), as proven in cnaddablx 19886; an Abelian group is a group as proven in ablgrp 19803. Other structures include groups, including unital rings (df-ring 20232) and fields (df-field 20732). (Contributed by NM, 17-Oct-2012.) (Revised by Mario Carneiro, 6-Jan-2015.) |
| ⊢ Grp = {𝑔 ∈ Mnd ∣ ∀𝑎 ∈ (Base‘𝑔)∃𝑚 ∈ (Base‘𝑔)(𝑚(+g‘𝑔)𝑎) = (0g‘𝑔)} | ||
| Definition | df-minusg 18955* | Define inverse of group element. (Contributed by NM, 24-Aug-2011.) |
| ⊢ invg = (𝑔 ∈ V ↦ (𝑥 ∈ (Base‘𝑔) ↦ (℩𝑤 ∈ (Base‘𝑔)(𝑤(+g‘𝑔)𝑥) = (0g‘𝑔)))) | ||
| Definition | df-sbg 18956* | Define group subtraction (also called division for multiplicative groups). (Contributed by NM, 31-Mar-2014.) |
| ⊢ -g = (𝑔 ∈ V ↦ (𝑥 ∈ (Base‘𝑔), 𝑦 ∈ (Base‘𝑔) ↦ (𝑥(+g‘𝑔)((invg‘𝑔)‘𝑦)))) | ||
| Theorem | isgrp 18957* | The predicate "is a group". (This theorem demonstrates the use of symbols as variable names, first proposed by FL in 2010.) (Contributed by NM, 17-Oct-2012.) (Revised by Mario Carneiro, 6-Jan-2015.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ 0 = (0g‘𝐺) ⇒ ⊢ (𝐺 ∈ Grp ↔ (𝐺 ∈ Mnd ∧ ∀𝑎 ∈ 𝐵 ∃𝑚 ∈ 𝐵 (𝑚 + 𝑎) = 0 )) | ||
| Theorem | grpmnd 18958 | A group is a monoid. (Contributed by Mario Carneiro, 6-Jan-2015.) |
| ⊢ (𝐺 ∈ Grp → 𝐺 ∈ Mnd) | ||
| Theorem | grpcl 18959 | Closure of the operation of a group. (Contributed by NM, 14-Aug-2011.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) ⇒ ⊢ ((𝐺 ∈ Grp ∧ 𝑋 ∈ 𝐵 ∧ 𝑌 ∈ 𝐵) → (𝑋 + 𝑌) ∈ 𝐵) | ||
| Theorem | grpass 18960 | A group operation is associative. (Contributed by NM, 14-Aug-2011.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) ⇒ ⊢ ((𝐺 ∈ Grp ∧ (𝑋 ∈ 𝐵 ∧ 𝑌 ∈ 𝐵 ∧ 𝑍 ∈ 𝐵)) → ((𝑋 + 𝑌) + 𝑍) = (𝑋 + (𝑌 + 𝑍))) | ||
| Theorem | grpinvex 18961* | Every member of a group has a left inverse. (Contributed by NM, 16-Aug-2011.) (Revised by Mario Carneiro, 6-Jan-2015.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ 0 = (0g‘𝐺) ⇒ ⊢ ((𝐺 ∈ Grp ∧ 𝑋 ∈ 𝐵) → ∃𝑦 ∈ 𝐵 (𝑦 + 𝑋) = 0 ) | ||
| Theorem | grpideu 18962* | The two-sided identity element of a group is unique. Lemma 2.2.1(a) of [Herstein] p. 55. (Contributed by NM, 16-Aug-2011.) (Revised by Mario Carneiro, 8-Dec-2014.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ 0 = (0g‘𝐺) ⇒ ⊢ (𝐺 ∈ Grp → ∃!𝑢 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑢 + 𝑥) = 𝑥 ∧ (𝑥 + 𝑢) = 𝑥)) | ||
| Theorem | grpassd 18963 | A group operation is associative. (Contributed by SN, 29-Jan-2025.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ (𝜑 → 𝐺 ∈ Grp) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) & ⊢ (𝜑 → 𝑍 ∈ 𝐵) ⇒ ⊢ (𝜑 → ((𝑋 + 𝑌) + 𝑍) = (𝑋 + (𝑌 + 𝑍))) | ||
| Theorem | grpmndd 18964 | A group is a monoid. (Contributed by SN, 1-Jun-2024.) |
| ⊢ (𝜑 → 𝐺 ∈ Grp) ⇒ ⊢ (𝜑 → 𝐺 ∈ Mnd) | ||
| Theorem | grpcld 18965 | Closure of the operation of a group. (Contributed by SN, 29-Jul-2024.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ (𝜑 → 𝐺 ∈ Grp) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) & ⊢ (𝜑 → 𝑌 ∈ 𝐵) ⇒ ⊢ (𝜑 → (𝑋 + 𝑌) ∈ 𝐵) | ||
| Theorem | grpplusf 18966 | The group addition operation is a function. (Contributed by Mario Carneiro, 14-Aug-2015.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ 𝐹 = (+𝑓‘𝐺) ⇒ ⊢ (𝐺 ∈ Grp → 𝐹:(𝐵 × 𝐵)⟶𝐵) | ||
| Theorem | grpplusfo 18967 | The group addition operation is a function onto the base set/set of group elements. (Contributed by NM, 30-Oct-2006.) (Revised by AV, 30-Aug-2021.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ 𝐹 = (+𝑓‘𝐺) ⇒ ⊢ (𝐺 ∈ Grp → 𝐹:(𝐵 × 𝐵)–onto→𝐵) | ||
| Theorem | resgrpplusfrn 18968 | The underlying set of a group operation which is a restriction of a structure. (Contributed by Paul Chapman, 25-Mar-2008.) (Revised by AV, 30-Aug-2021.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ 𝐻 = (𝐺 ↾s 𝑆) & ⊢ 𝐹 = (+𝑓‘𝐻) ⇒ ⊢ ((𝐻 ∈ Grp ∧ 𝑆 ⊆ 𝐵) → 𝑆 = ran 𝐹) | ||
| Theorem | grppropd 18969* | If two structures have the same group components (properties), one is a group iff the other one is. (Contributed by Stefan O'Rear, 27-Nov-2014.) (Revised by Mario Carneiro, 2-Oct-2015.) |
| ⊢ (𝜑 → 𝐵 = (Base‘𝐾)) & ⊢ (𝜑 → 𝐵 = (Base‘𝐿)) & ⊢ ((𝜑 ∧ (𝑥 ∈ 𝐵 ∧ 𝑦 ∈ 𝐵)) → (𝑥(+g‘𝐾)𝑦) = (𝑥(+g‘𝐿)𝑦)) ⇒ ⊢ (𝜑 → (𝐾 ∈ Grp ↔ 𝐿 ∈ Grp)) | ||
| Theorem | grpprop 18970 | If two structures have the same group components (properties), one is a group iff the other one is. (Contributed by NM, 11-Oct-2013.) |
| ⊢ (Base‘𝐾) = (Base‘𝐿) & ⊢ (+g‘𝐾) = (+g‘𝐿) ⇒ ⊢ (𝐾 ∈ Grp ↔ 𝐿 ∈ Grp) | ||
| Theorem | grppropstr 18971 | Generalize a specific 2-element group 𝐿 to show that any set 𝐾 with the same (relevant) properties is also a group. (Contributed by NM, 28-Oct-2012.) (Revised by Mario Carneiro, 6-Jan-2015.) |
| ⊢ (Base‘𝐾) = 𝐵 & ⊢ (+g‘𝐾) = + & ⊢ 𝐿 = {〈(Base‘ndx), 𝐵〉, 〈(+g‘ndx), + 〉} ⇒ ⊢ (𝐾 ∈ Grp ↔ 𝐿 ∈ Grp) | ||
| Theorem | grpss 18972 | Show that a structure extending a constructed group (e.g., a ring) is also a group. This allows to prove that a constructed potential ring 𝑅 is a group before we know that it is also a ring. (Theorem ringgrp 20235, on the other hand, requires that we know in advance that 𝑅 is a ring.) (Contributed by NM, 11-Oct-2013.) |
| ⊢ 𝐺 = {〈(Base‘ndx), 𝐵〉, 〈(+g‘ndx), + 〉} & ⊢ 𝑅 ∈ V & ⊢ 𝐺 ⊆ 𝑅 & ⊢ Fun 𝑅 ⇒ ⊢ (𝐺 ∈ Grp ↔ 𝑅 ∈ Grp) | ||
| Theorem | isgrpd2e 18973* | Deduce a group from its properties. In this version of isgrpd2 18974, we don't assume there is an expression for the inverse of 𝑥. (Contributed by NM, 10-Aug-2013.) |
| ⊢ (𝜑 → 𝐵 = (Base‘𝐺)) & ⊢ (𝜑 → + = (+g‘𝐺)) & ⊢ (𝜑 → 0 = (0g‘𝐺)) & ⊢ (𝜑 → 𝐺 ∈ Mnd) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐵) → ∃𝑦 ∈ 𝐵 (𝑦 + 𝑥) = 0 ) ⇒ ⊢ (𝜑 → 𝐺 ∈ Grp) | ||
| Theorem | isgrpd2 18974* | Deduce a group from its properties. 𝑁 (negative) is normally dependent on 𝑥 i.e. read it as 𝑁(𝑥). Note: normally we don't use a 𝜑 antecedent on hypotheses that name structure components, since they can be eliminated with eqid 2737, but we make an exception for theorems such as isgrpd2 18974, ismndd 18769, and islmodd 20864 since theorems using them often rewrite the structure components. (Contributed by NM, 10-Aug-2013.) |
| ⊢ (𝜑 → 𝐵 = (Base‘𝐺)) & ⊢ (𝜑 → + = (+g‘𝐺)) & ⊢ (𝜑 → 0 = (0g‘𝐺)) & ⊢ (𝜑 → 𝐺 ∈ Mnd) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐵) → 𝑁 ∈ 𝐵) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐵) → (𝑁 + 𝑥) = 0 ) ⇒ ⊢ (𝜑 → 𝐺 ∈ Grp) | ||
| Theorem | isgrpde 18975* | Deduce a group from its properties. In this version of isgrpd 18976, we don't assume there is an expression for the inverse of 𝑥. (Contributed by NM, 6-Jan-2015.) |
| ⊢ (𝜑 → 𝐵 = (Base‘𝐺)) & ⊢ (𝜑 → + = (+g‘𝐺)) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐵 ∧ 𝑦 ∈ 𝐵) → (𝑥 + 𝑦) ∈ 𝐵) & ⊢ ((𝜑 ∧ (𝑥 ∈ 𝐵 ∧ 𝑦 ∈ 𝐵 ∧ 𝑧 ∈ 𝐵)) → ((𝑥 + 𝑦) + 𝑧) = (𝑥 + (𝑦 + 𝑧))) & ⊢ (𝜑 → 0 ∈ 𝐵) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐵) → ( 0 + 𝑥) = 𝑥) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐵) → ∃𝑦 ∈ 𝐵 (𝑦 + 𝑥) = 0 ) ⇒ ⊢ (𝜑 → 𝐺 ∈ Grp) | ||
| Theorem | isgrpd 18976* | Deduce a group from its properties. Unlike isgrpd2 18974, this one goes straight from the base properties rather than going through Mnd. 𝑁 (negative) is normally dependent on 𝑥 i.e. read it as 𝑁(𝑥). (Contributed by NM, 6-Jun-2013.) (Revised by Mario Carneiro, 6-Jan-2015.) |
| ⊢ (𝜑 → 𝐵 = (Base‘𝐺)) & ⊢ (𝜑 → + = (+g‘𝐺)) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐵 ∧ 𝑦 ∈ 𝐵) → (𝑥 + 𝑦) ∈ 𝐵) & ⊢ ((𝜑 ∧ (𝑥 ∈ 𝐵 ∧ 𝑦 ∈ 𝐵 ∧ 𝑧 ∈ 𝐵)) → ((𝑥 + 𝑦) + 𝑧) = (𝑥 + (𝑦 + 𝑧))) & ⊢ (𝜑 → 0 ∈ 𝐵) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐵) → ( 0 + 𝑥) = 𝑥) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐵) → 𝑁 ∈ 𝐵) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐵) → (𝑁 + 𝑥) = 0 ) ⇒ ⊢ (𝜑 → 𝐺 ∈ Grp) | ||
| Theorem | isgrpi 18977* | Properties that determine a group. 𝑁 (negative) is normally dependent on 𝑥 i.e. read it as 𝑁(𝑥). (Contributed by NM, 3-Sep-2011.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ ((𝑥 ∈ 𝐵 ∧ 𝑦 ∈ 𝐵) → (𝑥 + 𝑦) ∈ 𝐵) & ⊢ ((𝑥 ∈ 𝐵 ∧ 𝑦 ∈ 𝐵 ∧ 𝑧 ∈ 𝐵) → ((𝑥 + 𝑦) + 𝑧) = (𝑥 + (𝑦 + 𝑧))) & ⊢ 0 ∈ 𝐵 & ⊢ (𝑥 ∈ 𝐵 → ( 0 + 𝑥) = 𝑥) & ⊢ (𝑥 ∈ 𝐵 → 𝑁 ∈ 𝐵) & ⊢ (𝑥 ∈ 𝐵 → (𝑁 + 𝑥) = 0 ) ⇒ ⊢ 𝐺 ∈ Grp | ||
| Theorem | grpsgrp 18978 | A group is a semigroup. (Contributed by AV, 28-Aug-2021.) |
| ⊢ (𝐺 ∈ Grp → 𝐺 ∈ Smgrp) | ||
| Theorem | grpmgmd 18979 | A group is a magma, deduction form. (Contributed by SN, 14-Apr-2025.) |
| ⊢ (𝜑 → 𝐺 ∈ Grp) ⇒ ⊢ (𝜑 → 𝐺 ∈ Mgm) | ||
| Theorem | dfgrp2 18980* | 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 18954, based on the definition of a monoid which provides a left and a right identity. (Contributed by AV, 28-Aug-2021.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) ⇒ ⊢ (𝐺 ∈ Grp ↔ (𝐺 ∈ Smgrp ∧ ∃𝑛 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖 ∈ 𝐵 (𝑖 + 𝑥) = 𝑛))) | ||
| Theorem | dfgrp2e 18981* | Alternate definition of a group as a set with a closed, associative operation, a left identity and a left inverse for each element. Alternate definition in [Lang] p. 7. (Contributed by NM, 10-Oct-2006.) (Revised by AV, 28-Aug-2021.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) ⇒ ⊢ (𝐺 ∈ Grp ↔ (∀𝑥 ∈ 𝐵 ∀𝑦 ∈ 𝐵 ((𝑥 + 𝑦) ∈ 𝐵 ∧ ∀𝑧 ∈ 𝐵 ((𝑥 + 𝑦) + 𝑧) = (𝑥 + (𝑦 + 𝑧))) ∧ ∃𝑛 ∈ 𝐵 ∀𝑥 ∈ 𝐵 ((𝑛 + 𝑥) = 𝑥 ∧ ∃𝑖 ∈ 𝐵 (𝑖 + 𝑥) = 𝑛))) | ||
| Theorem | isgrpix 18982* | Properties that determine a group. Read 𝑁 as 𝑁(𝑥). Note: This theorem has hard-coded structure indices for demonstration purposes. It is not intended for general use. (New usage is discouraged.) (Contributed by NM, 4-Sep-2011.) |
| ⊢ 𝐵 ∈ V & ⊢ + ∈ V & ⊢ 𝐺 = {〈1, 𝐵〉, 〈2, + 〉} & ⊢ ((𝑥 ∈ 𝐵 ∧ 𝑦 ∈ 𝐵) → (𝑥 + 𝑦) ∈ 𝐵) & ⊢ ((𝑥 ∈ 𝐵 ∧ 𝑦 ∈ 𝐵 ∧ 𝑧 ∈ 𝐵) → ((𝑥 + 𝑦) + 𝑧) = (𝑥 + (𝑦 + 𝑧))) & ⊢ 0 ∈ 𝐵 & ⊢ (𝑥 ∈ 𝐵 → ( 0 + 𝑥) = 𝑥) & ⊢ (𝑥 ∈ 𝐵 → 𝑁 ∈ 𝐵) & ⊢ (𝑥 ∈ 𝐵 → (𝑁 + 𝑥) = 0 ) ⇒ ⊢ 𝐺 ∈ Grp | ||
| Theorem | grpidcl 18983 | The identity element of a group belongs to the group. (Contributed by NM, 27-Aug-2011.) (Revised by Mario Carneiro, 27-Dec-2014.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ 0 = (0g‘𝐺) ⇒ ⊢ (𝐺 ∈ Grp → 0 ∈ 𝐵) | ||
| Theorem | grpbn0 18984 | The base set of a group is not empty. (Contributed by Szymon Jaroszewicz, 3-Apr-2007.) |
| ⊢ 𝐵 = (Base‘𝐺) ⇒ ⊢ (𝐺 ∈ Grp → 𝐵 ≠ ∅) | ||
| Theorem | grplid 18985 | The identity element of a group is a left identity. (Contributed by NM, 18-Aug-2011.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ 0 = (0g‘𝐺) ⇒ ⊢ ((𝐺 ∈ Grp ∧ 𝑋 ∈ 𝐵) → ( 0 + 𝑋) = 𝑋) | ||
| Theorem | grprid 18986 | The identity element of a group is a right identity. (Contributed by NM, 18-Aug-2011.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ 0 = (0g‘𝐺) ⇒ ⊢ ((𝐺 ∈ Grp ∧ 𝑋 ∈ 𝐵) → (𝑋 + 0 ) = 𝑋) | ||
| Theorem | grplidd 18987 | The identity element of a group is a left identity. Deduction associated with grplid 18985. (Contributed by SN, 29-Jan-2025.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ 0 = (0g‘𝐺) & ⊢ (𝜑 → 𝐺 ∈ Grp) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) ⇒ ⊢ (𝜑 → ( 0 + 𝑋) = 𝑋) | ||
| Theorem | grpridd 18988 | The identity element of a group is a right identity. Deduction associated with grprid 18986. (Contributed by SN, 29-Jan-2025.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ 0 = (0g‘𝐺) & ⊢ (𝜑 → 𝐺 ∈ Grp) & ⊢ (𝜑 → 𝑋 ∈ 𝐵) ⇒ ⊢ (𝜑 → (𝑋 + 0 ) = 𝑋) | ||
| Theorem | grpn0 18989 | A group is not empty. (Contributed by Szymon Jaroszewicz, 3-Apr-2007.) (Revised by Mario Carneiro, 2-Dec-2014.) |
| ⊢ (𝐺 ∈ Grp → 𝐺 ≠ ∅) | ||
| Theorem | hashfingrpnn 18990 | A finite group has positive integer size. (Contributed by Rohan Ridenour, 3-Aug-2023.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ (𝜑 → 𝐺 ∈ Grp) & ⊢ (𝜑 → 𝐵 ∈ Fin) ⇒ ⊢ (𝜑 → (♯‘𝐵) ∈ ℕ) | ||
| Theorem | grprcan 18991 | Right cancellation law for groups. (Contributed by NM, 24-Aug-2011.) (Proof shortened by Mario Carneiro, 6-Jan-2015.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) ⇒ ⊢ ((𝐺 ∈ Grp ∧ (𝑋 ∈ 𝐵 ∧ 𝑌 ∈ 𝐵 ∧ 𝑍 ∈ 𝐵)) → ((𝑋 + 𝑍) = (𝑌 + 𝑍) ↔ 𝑋 = 𝑌)) | ||
| Theorem | grpinveu 18992* | The left inverse element of a group is unique. Lemma 2.2.1(b) of [Herstein] p. 55. (Contributed by NM, 24-Aug-2011.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ 0 = (0g‘𝐺) ⇒ ⊢ ((𝐺 ∈ Grp ∧ 𝑋 ∈ 𝐵) → ∃!𝑦 ∈ 𝐵 (𝑦 + 𝑋) = 0 ) | ||
| Theorem | grpid 18993 | Two ways of saying that an element of a group is the identity element. Provides a convenient way to compute the value of the identity element. (Contributed by NM, 24-Aug-2011.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ 0 = (0g‘𝐺) ⇒ ⊢ ((𝐺 ∈ Grp ∧ 𝑋 ∈ 𝐵) → ((𝑋 + 𝑋) = 𝑋 ↔ 0 = 𝑋)) | ||
| Theorem | isgrpid2 18994 | Properties showing that an element 𝑍 is the identity element of a group. (Contributed by NM, 7-Aug-2013.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ 0 = (0g‘𝐺) ⇒ ⊢ (𝐺 ∈ Grp → ((𝑍 ∈ 𝐵 ∧ (𝑍 + 𝑍) = 𝑍) ↔ 0 = 𝑍)) | ||
| Theorem | grpidd2 18995* | Deduce the identity element of a group from its properties. Useful in conjunction with isgrpd 18976. (Contributed by Mario Carneiro, 14-Jun-2015.) |
| ⊢ (𝜑 → 𝐵 = (Base‘𝐺)) & ⊢ (𝜑 → + = (+g‘𝐺)) & ⊢ (𝜑 → 0 ∈ 𝐵) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝐵) → ( 0 + 𝑥) = 𝑥) & ⊢ (𝜑 → 𝐺 ∈ Grp) ⇒ ⊢ (𝜑 → 0 = (0g‘𝐺)) | ||
| Theorem | grpinvfval 18996* | The inverse function of a group. For a shorter proof using ax-rep 5279, see grpinvfvalALT 18997. (Contributed by NM, 24-Aug-2011.) (Revised by Mario Carneiro, 7-Aug-2013.) Remove dependency on ax-rep 5279. (Revised by Rohan Ridenour, 13-Aug-2023.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ 0 = (0g‘𝐺) & ⊢ 𝑁 = (invg‘𝐺) ⇒ ⊢ 𝑁 = (𝑥 ∈ 𝐵 ↦ (℩𝑦 ∈ 𝐵 (𝑦 + 𝑥) = 0 )) | ||
| Theorem | grpinvfvalALT 18997* | Shorter proof of grpinvfval 18996 using ax-rep 5279. (Contributed by NM, 24-Aug-2011.) (Revised by Mario Carneiro, 7-Aug-2013.) (Proof modification is discouraged.) (New usage is discouraged.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ 0 = (0g‘𝐺) & ⊢ 𝑁 = (invg‘𝐺) ⇒ ⊢ 𝑁 = (𝑥 ∈ 𝐵 ↦ (℩𝑦 ∈ 𝐵 (𝑦 + 𝑥) = 0 )) | ||
| Theorem | grpinvval 18998* | The inverse of a group element. (Contributed by NM, 24-Aug-2011.) (Revised by Mario Carneiro, 7-Aug-2013.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ + = (+g‘𝐺) & ⊢ 0 = (0g‘𝐺) & ⊢ 𝑁 = (invg‘𝐺) ⇒ ⊢ (𝑋 ∈ 𝐵 → (𝑁‘𝑋) = (℩𝑦 ∈ 𝐵 (𝑦 + 𝑋) = 0 )) | ||
| Theorem | grpinvfn 18999 | Functionality of the group inverse function. (Contributed by Stefan O'Rear, 21-Mar-2015.) |
| ⊢ 𝐵 = (Base‘𝐺) & ⊢ 𝑁 = (invg‘𝐺) ⇒ ⊢ 𝑁 Fn 𝐵 | ||
| Theorem | grpinvfvi 19000 | The group inverse function is compatible with identity-function protection. (Contributed by Stefan O'Rear, 21-Mar-2015.) |
| ⊢ 𝑁 = (invg‘𝐺) ⇒ ⊢ 𝑁 = (invg‘( I ‘𝐺)) | ||
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