mathlib3 documentation

group_theory.finiteness

Finitely generated monoids and groups #

THIS FILE IS SYNCHRONIZED WITH MATHLIB4. Any changes to this file require a corresponding PR to mathlib4.

We define finitely generated monoids and groups. See also submodule.fg and module.finite for finitely-generated modules.

Main definition #

Monoids and submonoids #

source
def add_submonoid.fg {M : Type u_1} [add_monoid M] (P : add_submonoid M) :
Prop

An additive submonoid of N is finitely generated if it is the closure of a finite subset of M.

Equations
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def submonoid.fg {M : Type u_1} [monoid M] (P : submonoid M) :
Prop

A submonoid of M is finitely generated if it is the closure of a finite subset of M.

Equations
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theorem submonoid.fg_iff {M : Type u_1} [monoid M] (P : submonoid M) :
P.fg ↔ ∃ (S : set M), submonoid.closure S = P ∧ S.finite

An equivalent expression of submonoid.fg in terms of set.finite instead of finset.

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theorem add_submonoid.fg_iff {M : Type u_1} [add_monoid M] (P : add_submonoid M) :
P.fg ↔ ∃ (S : set M), add_submonoid.closure S = P ∧ S.finite

An equivalent expression of add_submonoid.fg in terms of set.finite instead of finset.

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theorem submonoid.fg_iff_add_fg {M : Type u_1} [monoid M] (P : submonoid M) :
P.fg ↔ (⇑submonoid.to_add_submonoid P).fg
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theorem add_submonoid.fg_iff_mul_fg {N : Type u_2} [add_monoid N] (P : add_submonoid N) :
P.fg ↔ (⇑add_submonoid.to_submonoid P).fg
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@[class]
structure monoid.fg (M : Type u_1) [monoid M] :
Prop

A monoid is finitely generated if it is finitely generated as a submonoid of itself.

Instances of this typeclass
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@[class]
structure add_monoid.fg (N : Type u_2) [add_monoid N] :
Prop

An additive monoid is finitely generated if it is finitely generated as an additive submonoid of itself.

Instances of this typeclass
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theorem monoid.fg_def {M : Type u_1} [monoid M] :
monoid.fg M ↔ ⊤.fg
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theorem add_monoid.fg_def {N : Type u_2} [add_monoid N] :
add_monoid.fg N ↔ ⊤.fg
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theorem monoid.fg_iff {M : Type u_1} [monoid M] :
monoid.fg M ↔ ∃ (S : set M), submonoid.closure S = ⊤ ∧ S.finite

An equivalent expression of monoid.fg in terms of set.finite instead of finset.

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theorem add_monoid.fg_iff {M : Type u_1} [add_monoid M] :
add_monoid.fg M ↔ ∃ (S : set M), add_submonoid.closure S = ⊤ ∧ S.finite

An equivalent expression of add_monoid.fg in terms of set.finite instead of finset.

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theorem monoid.fg_iff_add_fg {M : Type u_1} [monoid M] :
monoid.fg M ↔ add_monoid.fg (additive M)
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theorem add_monoid.fg_iff_mul_fg {N : Type u_2} [add_monoid N] :
add_monoid.fg N ↔ monoid.fg (multiplicative N)
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@[protected, instance]
def add_monoid.fg_of_monoid_fg {M : Type u_1} [monoid M] [monoid.fg M] :
add_monoid.fg (additive M)
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@[protected, instance]
def monoid.fg_of_add_monoid_fg {N : Type u_2} [add_monoid N] [add_monoid.fg N] :
monoid.fg (multiplicative N)
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@[protected, instance]
def monoid.fg_of_finite {M : Type u_1} [monoid M] [finite M] :
monoid.fg M
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@[protected, instance]
def add_monoid.fg_of_finite {M : Type u_1} [add_monoid M] [finite M] :
add_monoid.fg M
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theorem submonoid.fg.map {M : Type u_1} [monoid M] {M' : Type u_2} [monoid M'] {P : submonoid M} (h : P.fg) (e : M →* M') :
(submonoid.map e P).fg
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theorem add_submonoid.fg.map {M : Type u_1} [add_monoid M] {M' : Type u_2} [add_monoid M'] {P : add_submonoid M} (h : P.fg) (e : M →+ M') :
(add_submonoid.map e P).fg
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theorem add_submonoid.fg.map_injective {M : Type u_1} [add_monoid M] {M' : Type u_2} [add_monoid M'] {P : add_submonoid M} (e : M →+ M') (he : function.injective ⇑e) (h : (add_submonoid.map e P).fg) :
P.fg
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theorem submonoid.fg.map_injective {M : Type u_1} [monoid M] {M' : Type u_2} [monoid M'] {P : submonoid M} (e : M →* M') (he : function.injective ⇑e) (h : (submonoid.map e P).fg) :
P.fg
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@[simp]
theorem add_monoid.fg_iff_add_submonoid_fg {M : Type u_1} [add_monoid M] (N : add_submonoid M) :
add_monoid.fg ↥N ↔ N.fg
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@[simp]
theorem monoid.fg_iff_submonoid_fg {M : Type u_1} [monoid M] (N : submonoid M) :
monoid.fg ↥N ↔ N.fg
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theorem add_monoid.fg_of_surjective {M : Type u_1} [add_monoid M] {M' : Type u_2} [add_monoid M'] [add_monoid.fg M] (f : M →+ M') (hf : function.surjective ⇑f) :
add_monoid.fg M'
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theorem monoid.fg_of_surjective {M : Type u_1} [monoid M] {M' : Type u_2} [monoid M'] [monoid.fg M] (f : M →* M') (hf : function.surjective ⇑f) :
monoid.fg M'
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@[protected, instance]
def monoid.fg_range {M : Type u_1} [monoid M] {M' : Type u_2} [monoid M'] [monoid.fg M] (f : M →* M') :
monoid.fg ↥(monoid_hom.mrange f)
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@[protected, instance]
def add_monoid.fg_range {M : Type u_1} [add_monoid M] {M' : Type u_2} [add_monoid M'] [add_monoid.fg M] (f : M →+ M') :
add_monoid.fg ↥(add_monoid_hom.mrange f)
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theorem submonoid.powers_fg {M : Type u_1} [monoid M] (r : M) :
(submonoid.powers r).fg
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theorem add_submonoid.multiples_fg {M : Type u_1} [add_monoid M] (r : M) :
(add_submonoid.multiples r).fg
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@[protected, instance]
def add_monoid.multiples_fg {M : Type u_1} [add_monoid M] (r : M) :
add_monoid.fg ↥(add_submonoid.multiples r)
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@[protected, instance]
def monoid.powers_fg {M : Type u_1} [monoid M] (r : M) :
monoid.fg ↥(submonoid.powers r)
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@[protected, instance]
def add_monoid.closure_finset_fg {M : Type u_1} [add_monoid M] (s : finset M) :
add_monoid.fg ↥(add_submonoid.closure ↑s)
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@[protected, instance]
def monoid.closure_finset_fg {M : Type u_1} [monoid M] (s : finset M) :
monoid.fg ↥(submonoid.closure ↑s)
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@[protected, instance]
def add_monoid.closure_finite_fg {M : Type u_1} [add_monoid M] (s : set M) [finite ↥s] :
add_monoid.fg ↥(add_submonoid.closure s)
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@[protected, instance]
def monoid.closure_finite_fg {M : Type u_1} [monoid M] (s : set M) [finite ↥s] :
monoid.fg ↥(submonoid.closure s)

Groups and subgroups #

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def add_subgroup.fg {G : Type u_3} [add_group G] (P : add_subgroup G) :
Prop

An additive subgroup of H is finitely generated if it is the closure of a finite subset of H.

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def subgroup.fg {G : Type u_3} [group G] (P : subgroup G) :
Prop

A subgroup of G is finitely generated if it is the closure of a finite subset of G.

Equations
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theorem subgroup.fg_iff {G : Type u_3} [group G] (P : subgroup G) :
P.fg ↔ ∃ (S : set G), subgroup.closure S = P ∧ S.finite

An equivalent expression of subgroup.fg in terms of set.finite instead of finset.

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theorem add_subgroup.fg_iff {G : Type u_3} [add_group G] (P : add_subgroup G) :
P.fg ↔ ∃ (S : set G), add_subgroup.closure S = P ∧ S.finite

An equivalent expression of add_subgroup.fg in terms of set.finite instead of finset.

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theorem subgroup.fg_iff_submonoid_fg {G : Type u_3} [group G] (P : subgroup G) :
P.fg ↔ P.to_submonoid.fg

A subgroup is finitely generated if and only if it is finitely generated as a submonoid.

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theorem add_subgroup.fg_iff_add_submonoid.fg {G : Type u_3} [add_group G] (P : add_subgroup G) :
P.fg ↔ P.to_add_submonoid.fg

An additive subgroup is finitely generated if and only if it is finitely generated as an additive submonoid.

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theorem subgroup.fg_iff_add_fg {G : Type u_3} [group G] (P : subgroup G) :
P.fg ↔ (⇑subgroup.to_add_subgroup P).fg
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theorem add_subgroup.fg_iff_mul_fg {H : Type u_4} [add_group H] (P : add_subgroup H) :
P.fg ↔ (⇑add_subgroup.to_subgroup P).fg
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@[class]
structure group.fg (G : Type u_3) [group G] :
Prop

A group is finitely generated if it is finitely generated as a submonoid of itself.

Instances of this typeclass
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@[class]
structure add_group.fg (H : Type u_4) [add_group H] :
Prop

An additive group is finitely generated if it is finitely generated as an additive submonoid of itself.

Instances of this typeclass
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theorem group.fg_def {G : Type u_3} [group G] :
group.fg G ↔ ⊤.fg
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theorem add_group.fg_def {H : Type u_4} [add_group H] :
add_group.fg H ↔ ⊤.fg
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theorem add_group.fg_iff {G : Type u_3} [add_group G] :
add_group.fg G ↔ ∃ (S : set G), add_subgroup.closure S = ⊤ ∧ S.finite

An equivalent expression of add_group.fg in terms of set.finite instead of finset.

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theorem group.fg_iff {G : Type u_3} [group G] :
group.fg G ↔ ∃ (S : set G), subgroup.closure S = ⊤ ∧ S.finite

An equivalent expression of group.fg in terms of set.finite instead of finset.

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theorem add_group.fg_iff' {G : Type u_3} [add_group G] :
add_group.fg G ↔ ∃ (n : ℕ) (S : finset G), S.card = n ∧ add_subgroup.closure ↑S = ⊤
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theorem group.fg_iff' {G : Type u_3} [group G] :
group.fg G ↔ ∃ (n : ℕ) (S : finset G), S.card = n ∧ subgroup.closure ↑S = ⊤
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theorem group.fg_iff_monoid.fg {G : Type u_3} [group G] :
group.fg G ↔ monoid.fg G

A group is finitely generated if and only if it is finitely generated as a monoid.

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theorem add_group.fg_iff_add_monoid.fg {G : Type u_3} [add_group G] :
add_group.fg G ↔ add_monoid.fg G

An additive group is finitely generated if and only if it is finitely generated as an additive monoid.

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theorem group_fg.iff_add_fg {G : Type u_3} [group G] :
group.fg G ↔ add_group.fg (additive G)
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theorem add_group.fg_iff_mul_fg {H : Type u_4} [add_group H] :
add_group.fg H ↔ group.fg (multiplicative H)
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@[protected, instance]
def add_group.fg_of_group_fg {G : Type u_3} [group G] [group.fg G] :
add_group.fg (additive G)
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@[protected, instance]
def group.fg_of_mul_group_fg {H : Type u_4} [add_group H] [add_group.fg H] :
group.fg (multiplicative H)
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@[protected, instance]
def group.fg_of_finite {G : Type u_3} [group G] [finite G] :
group.fg G
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@[protected, instance]
def add_group.fg_of_finite {G : Type u_3} [add_group G] [finite G] :
add_group.fg G
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theorem add_group.fg_of_surjective {G : Type u_3} [add_group G] {G' : Type u_1} [add_group G'] [hG : add_group.fg G] {f : G →+ G'} (hf : function.surjective ⇑f) :
add_group.fg G'
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theorem group.fg_of_surjective {G : Type u_3} [group G] {G' : Type u_1} [group G'] [hG : group.fg G] {f : G →* G'} (hf : function.surjective ⇑f) :
group.fg G'
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@[protected, instance]
def add_group.fg_range {G : Type u_3} [add_group G] {G' : Type u_1} [add_group G'] [add_group.fg G] (f : G →+ G') :
add_group.fg ↥(f.range)
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@[protected, instance]
def group.fg_range {G : Type u_3} [group G] {G' : Type u_1} [group G'] [group.fg G] (f : G →* G') :
group.fg ↥(f.range)
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@[protected, instance]
def add_group.closure_finset_fg {G : Type u_3} [add_group G] (s : finset G) :
add_group.fg ↥(add_subgroup.closure ↑s)
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@[protected, instance]
def group.closure_finset_fg {G : Type u_3} [group G] (s : finset G) :
group.fg ↥(subgroup.closure ↑s)
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@[protected, instance]
def add_group.closure_finite_fg {G : Type u_3} [add_group G] (s : set G) [finite ↥s] :
add_group.fg ↥(add_subgroup.closure s)
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@[protected, instance]
def group.closure_finite_fg {G : Type u_3} [group G] (s : set G) [finite ↥s] :
group.fg ↥(subgroup.closure s)
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noncomputable def add_group.rank (G : Type u_3) [add_group G] [h : add_group.fg G] :
ℕ

The minimum number of generators of an additive group

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noncomputable def group.rank (G : Type u_3) [group G] [h : group.fg G] :
ℕ

The minimum number of generators of a group.

Equations
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theorem group.rank_spec (G : Type u_3) [group G] [h : group.fg G] :
∃ (S : finset G), S.card = group.rank G ∧ subgroup.closure ↑S = ⊤
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theorem add_group.rank_spec (G : Type u_3) [add_group G] [h : add_group.fg G] :
∃ (S : finset G), S.card = add_group.rank G ∧ add_subgroup.closure ↑S = ⊤
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theorem add_group.rank_le (G : Type u_3) [add_group G] [h : add_group.fg G] {S : finset G} (hS : add_subgroup.closure ↑S = ⊤) :
add_group.rank G ≤ S.card
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theorem group.rank_le (G : Type u_3) [group G] [h : group.fg G] {S : finset G} (hS : subgroup.closure ↑S = ⊤) :
group.rank G ≤ S.card
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theorem add_group.rank_le_of_surjective {G : Type u_3} [add_group G] {G' : Type u_5} [add_group G'] [add_group.fg G] [add_group.fg G'] (f : G →+ G') (hf : function.surjective ⇑f) :
add_group.rank G' ≤ add_group.rank G
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theorem group.rank_le_of_surjective {G : Type u_3} [group G] {G' : Type u_5} [group G'] [group.fg G] [group.fg G'] (f : G →* G') (hf : function.surjective ⇑f) :
group.rank G' ≤ group.rank G
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theorem group.rank_range_le {G : Type u_3} [group G] {G' : Type u_5} [group G'] [group.fg G] {f : G →* G'} :
group.rank ↥(f.range) ≤ group.rank G
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theorem add_group.rank_range_le {G : Type u_3} [add_group G] {G' : Type u_5} [add_group G'] [add_group.fg G] {f : G →+ G'} :
add_group.rank ↥(f.range) ≤ add_group.rank G
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theorem group.rank_congr {G : Type u_3} [group G] {G' : Type u_5} [group G'] [group.fg G] [group.fg G'] (f : G ≃* G') :
group.rank G = group.rank G'
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theorem add_group.rank_congr {G : Type u_3} [add_group G] {G' : Type u_5} [add_group G'] [add_group.fg G] [add_group.fg G'] (f : G ≃+ G') :
add_group.rank G = add_group.rank G'
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theorem subgroup.rank_congr {G : Type u_3} [group G] {H K : subgroup G} [group.fg ↥H] [group.fg ↥K] (h : H = K) :
group.rank ↥H = group.rank ↥K
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theorem add_subgroup.rank_congr {G : Type u_3} [add_group G] {H K : add_subgroup G} [add_group.fg ↥H] [add_group.fg ↥K] (h : H = K) :
add_group.rank ↥H = add_group.rank ↥K
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theorem add_subgroup.rank_closure_finset_le_card {G : Type u_3} [add_group G] (s : finset G) :
add_group.rank ↥(add_subgroup.closure ↑s) ≤ s.card
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theorem subgroup.rank_closure_finset_le_card {G : Type u_3} [group G] (s : finset G) :
group.rank ↥(subgroup.closure ↑s) ≤ s.card
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theorem add_subgroup.rank_closure_finite_le_nat_card {G : Type u_3} [add_group G] (s : set G) [finite ↥s] :
add_group.rank ↥(add_subgroup.closure s) ≤ nat.card ↥s
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theorem subgroup.rank_closure_finite_le_nat_card {G : Type u_3} [group G] (s : set G) [finite ↥s] :
group.rank ↥(subgroup.closure s) ≤ nat.card ↥s
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@[protected, instance]
def quotient_group.fg {G : Type u_3} [group G] [group.fg G] (N : subgroup G) [N.normal] :
group.fg (G ⧸ N)
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@[protected, instance]
def quotient_add_group.fg {G : Type u_3} [add_group G] [add_group.fg G] (N : add_subgroup G) [N.normal] :
add_group.fg (G ⧸ N)