Products of tuples of elements in commutative monoids

Content created by Jonathan Prieto-Cubides, Egbert Rijke and Fredrik Bakke.

Created on 2022-05-24.
Last modified on 2023-06-10.

module group-theory.products-of-tuples-of-elements-commutative-monoids where
open import elementary-number-theory.natural-numbers

open import foundation.coproduct-types
open import foundation.function-types
open import foundation.unit-type
open import foundation.universe-levels

open import group-theory.commutative-monoids

open import univalent-combinatorics.counting
open import univalent-combinatorics.standard-finite-types


Given an unordered n-tuple of elements in a commutative monoid, we can define their product.


Products of ordered n-tuples of elements in commutative monoids

module _
  {l : Level} (M : Commutative-Monoid l)

  mul-fin-Commutative-Monoid :
    (n : )  (Fin n  type-Commutative-Monoid M)  type-Commutative-Monoid M
  mul-fin-Commutative-Monoid zero-ℕ x = unit-Commutative-Monoid M
  mul-fin-Commutative-Monoid (succ-ℕ n) x =
    mul-Commutative-Monoid M
      ( mul-fin-Commutative-Monoid n (x  inl))
      ( x (inr star))

  mul-count-Commutative-Monoid :
    {l2 : Level} {A : UU l2}  count A 
    (A  type-Commutative-Monoid M)  type-Commutative-Monoid M
  mul-count-Commutative-Monoid e x =
      ( number-of-elements-count e)
      ( x  map-equiv-count e)

  compute-permutation-mul-fin-Commutative-Monoid :
    (n : ℕ) (e : Fin n ≃ Fin n) (x : Fin n → type-Commutative-Monoid M) →
    Id ( mul-fin-Commutative-Monoid n (x ∘ map-equiv e))
       ( mul-fin-Commutative-Monoid n x)
  compute-permutation-mul-fin-Commutative-Monoid zero-ℕ e x = refl
  compute-permutation-mul-fin-Commutative-Monoid (succ-ℕ n) e x = {!!}

  compute-mul-double-counting-Commutative-Monoid :
    {l2 : Level} {A : UU l2} (e1 : count A) (e2 : count A) →
    (x : A → type-Commutative-Monoid M) →
    Id (mul-count-Commutative-Monoid e1 x) (mul-count-Commutative-Monoid e2 x)
  compute-mul-double-counting-Commutative-Monoid e1 e2 x = {!!}

Products of unordered n-tuples of elements in commutative monoids

module _
  {l : Level} (M : Commutative-Monoid l)

  mul-tuple-Commutative-Monoid :
    {n : ℕ} → unordered-tuple-Commutative-Monoid n M → type-Commutative-Monoid M
  mul-tuple-Commutative-Monoid {n} (pair I x) = {!!}

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