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group_basics fixes

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This commit is contained in:
Ulrik Buchholtz 2016-09-08 14:58:51 -04:00
parent 01f90ef944
commit af0b342de8
1 changed files with 6 additions and 6 deletions
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12
algebra/group_basics.hlean
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@ -16,14 +16,14 @@ namespace group
/-- Recall that a subtype of a type A is the same thing as a family of mere propositions over A. Thus, we define a subgroup of a group G to be a family of mere propositions over (the underlying type of) G, closed under the constants and operations --/
/-- Question: Why is this called subgroup_rel. Because it is a unary relation? --/
structure subgroup_rel.{u} (G : Group.{u}) : Type.{u+1} :=
(R : G → Prop.{u})
structure subgroup_rel.{u v} (G : Group.{u}) : Type.{max u (v+1)} :=
(R : G → Prop.{v})
(Rone : R one)
(Rmul : Π{g h}, R g → R h → R (g * h))
(Rinv : Π{g}, R g → R (g⁻¹))
/-- Every group G has at least two subgroups, the trivial subgroup containing only one, and the full subgroup. --/
definition trivial_subgroup.{u} (G : Group.{u}) : subgroup_rel.{u} G :=
definition trivial_subgroup.{u} (G : Group.{u}) : subgroup_rel.{u u} G :=
begin
fapply subgroup_rel.mk,
{ intro g, fapply trunctype.mk, exact (g = one), exact _ },
@ -34,7 +34,7 @@ namespace group
definition is_trivial_subgroup (G : Group) (R : subgroup_rel G) : Prop := sorry /- Π g, R g = trivial_subgroup g -/
definition full_subgroup (G : Group) : subgroup_rel G :=
definition full_subgroup.{u} (G : Group.{u}) : subgroup_rel.{u u} G :=
begin
fapply subgroup_rel.mk,
{ intro g, fapply trunctype.mk, exact g = g, exact _}, -- instead of the unit type, we take g = g, because the unit type is in Type₀ and not in Type.{u}
@ -103,7 +103,7 @@ namespace group
end kernels
/-- Now we should be able to show that if f is a homomorphism for which the kernel is trivial and the image is full, then f is an isomorphism, except that no one defined the proposition that f is an isomorphism :/ --/
definition is_iso_from_kertriv_imfull {G H : Group} (f : G →g H) : is_trivial_subgroup G (kernel f) → is_full_subgroup H (image_subgroup f) → unit /- replace unit by is_isomorphism f -/ := sorry
-- definition is_iso_from_kertriv_imfull {G H : Group} (f : G →g H) : is_trivial_subgroup G (kernel f) → is_full_subgroup H (image_subgroup f) → unit /- replace unit by is_isomorphism f -/ := sorry
/- #Normal subgroups -/
@ -124,7 +124,7 @@ namespace group
{ /-inverse is right inverse?-/ exact sorry},
end
definition inner_aut (G : Group) : G →g (G ≃g G) := sorry /-- h ↦ h * g * h⁻¹ --/
-- definition inner_aut (G : Group) : G →g (G ≃g G) := sorry /-- h ↦ h * g * h⁻¹ --/
/-- There is a problem with the following definition, namely that there is no mere proposition that says that N is normal --/
structure normal_subgroup_rel (G : Group) extends subgroup_rel G :=