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chore(group_theory/submonoid): split into 3 files (#3058)
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* `group_theory.submonoid.basic` contains the definition, `complete_lattice` structure, and some basic facts about `closure`;
* `group_theory.submonoid.operations` contains definitions of various operations on submonoids;
* `group_theory.submonoid.membership` contains various facts about membership in a submonoid or the submonoid closure of a set.
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urkud committed Jun 28, 2020
1 parent 4ad82e5 commit 2ec83dc
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Showing 7 changed files with 997 additions and 823 deletions.
4 changes: 2 additions & 2 deletions src/group_theory/subgroup.lean
Expand Up @@ -817,8 +817,8 @@ open set

lemma gsmul_mem (H : add_subgroup A) {x : A} (hx : x ∈ H) :
∀ n : ℤ, gsmul n x ∈ H
| (int.of_nat n) := add_submonoid.smul_mem H.to_add_submonoid hx n
| -[1+ n] := H.neg_mem' $ H.add_mem hx $ add_submonoid.smul_mem H.to_add_submonoid hx n
| (int.of_nat n) := add_submonoid.nsmul_mem H.to_add_submonoid hx n
| -[1+ n] := H.neg_mem' $ H.add_mem hx $ add_submonoid.nsmul_mem H.to_add_submonoid hx n

lemma sub_mem (H : add_subgroup A) {x y : A} (hx : x ∈ H) (hy : y ∈ H) : x - y ∈ H :=
H.add_mem hx (H.neg_mem hy)
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