mathlib documentation


The symmetric monoidal category structure on R-modules

Mostly this uses existing machinery in linear_algebra.tensor_product. We just need to provide a few small missing pieces to build the monoidal_category instance and then the symmetric_category instance.

If you're happy using the bundled Module R, it may be possible to mostly use this as an interface and not need to interact much with the implementation details.

def Module.monoidal_category.tensor_obj {R : Type u} [comm_ring R] (M : Module R) (N : Module R) :

(implementation) tensor product of R-modules


(implementation) tensor product of morphisms R-modules

theorem Module.monoidal_category.tensor_comp {R : Type u} [comm_ring R] {X₁ Y₁ Z₁ : Module R} {X₂ Y₂ Z₂ : Module R} (f₁ : X₁ Y₁) (f₂ : X₂ Y₂) (g₁ : Y₁ Z₁) (g₂ : Y₂ Z₂) :

The associator_naturality and pentagon lemmas below are very slow to elaborate.

We give them some help by expressing the lemmas first non-categorically, then using convert _aux using 1 to have the elaborator work as little as possible.

theorem Module.monoidal_category.associator_naturality {R : Type u} [comm_ring R] {X₁ : Module R} {X₂ : Module R} {X₃ : Module R} {Y₁ : Module R} {Y₂ : Module R} {Y₃ : Module R} (f₁ : X₁ Y₁) (f₂ : X₂ Y₂) (f₃ : X₃ Y₃) :

def Module.monoidal_category.left_unitor {R : Type u} [comm_ring R] (M : Module R) :
Module.of R (R M) M

(implementation) the left unitor for R-modules

def Module.monoidal_category.right_unitor {R : Type u} [comm_ring R] (M : Module R) :
Module.of R (M R) M

(implementation) the right unitor for R-modules


Remind ourselves that the monoidal unit, being just R, is still a commutative ring.

theorem Module.monoidal_category.hom_apply {R : Type u} [comm_ring R] {K L M N : Module R} (f : K L) (g : M N) (k : K) (m : M) :
(f g) (k ⊗ₜ[R] m) = f k ⊗ₜ[R] g m

theorem Module.monoidal_category.left_unitor_hom_apply {R : Type u} [comm_ring R] {M : Module R} (r : R) (m : M) :
((λ_ M).hom) (r ⊗ₜ[R] m) = r m

theorem Module.monoidal_category.right_unitor_hom_apply {R : Type u} [comm_ring R] {M : Module R} (m : M) (r : R) :
((ρ_ M).hom) (m ⊗ₜ[R] r) = r m

theorem Module.monoidal_category.associator_hom_apply {R : Type u} [comm_ring R] {M N K : Module R} (m : M) (n : N) (k : K) :
((α_ M N K).hom) (m ⊗ₜ[R] n ⊗ₜ[R] k) = m ⊗ₜ[R] (n ⊗ₜ[R] k)

(implementation) the braiding for R-modules

theorem Module.braiding_naturality {R : Type u} [comm_ring R] {X₁ X₂ Y₁ Y₂ : Module R} (f : X₁ Y₁) (g : X₂ Y₂) :
(f g) (Y₁.braiding Y₂).hom = (X₁.braiding X₂).hom (g f)

theorem Module.hexagon_forward {R : Type u} [comm_ring R] (X Y Z : Module R) :
(α_ X Y Z).hom (X.braiding (Y Z)).hom (α_ Y Z X).hom = ((X.braiding Y).hom 𝟙 Z) (α_ Y X Z).hom (𝟙 Y (X.braiding Z).hom)

theorem Module.hexagon_reverse {R : Type u} [comm_ring R] (X Y Z : Module R) :
(α_ X Y Z).inv ((X Y).braiding Z).hom (α_ Z X Y).inv = (𝟙 X (Y.braiding Z).hom) (α_ X Z Y).inv ((X.braiding Z).hom 𝟙 Y)

theorem Module.monoidal_category.braiding_hom_apply {R : Type u} [comm_ring R] {M N : Module R} (m : M) (n : N) :
((β_ M N).hom) (m ⊗ₜ[R] n) = n ⊗ₜ[R] m

theorem Module.monoidal_category.braiding_inv_apply {R : Type u} [comm_ring R] {M N : Module R} (m : M) (n : N) :
((β_ M N).inv) (n ⊗ₜ[R] m) = m ⊗ₜ[R] n