Dirichlet series of species of finite inhabited types

Content created by Fredrik Bakke and Victor Blanchi.

Created on 2023-05-22.
Last modified on 2023-05-22.

module species.dirichlet-series-species-of-finite-inhabited-types where
open import elementary-number-theory.natural-numbers

open import foundation.cartesian-product-types
open import foundation.dependent-pair-types
open import foundation.universe-levels

open import species.species-of-finite-inhabited-types

open import univalent-combinatorics.cycle-prime-decomposition-natural-numbers
open import univalent-combinatorics.finite-types
open import univalent-combinatorics.inhabited-finite-types


In classical mathematics, the Dirichlet series of a species of finite inhabited types T is the formal series in s :

Σ (n : ℕ∖{0}) (|T({1,...,n}| n^(-s) / n!))

If s is a negative integer, the categorified version of this formula is

Σ (F : 𝔽 ∖ {∅}), T (F) × (S → F)

We can generalize it to species of types as

Σ (U : UU) (T (U) × (S → U))

The interesting case is when s is a positive number. The categorified version of this formula then becomes

Σ ( n : ℕ ∖ {0}),
  ( Σ (F : UU-Fin n) , T (F) × (S → cycle-prime-decomposition-ℕ (n))

We have picked the concrete group cycle-prime-decomposition-ℕ (n) because it is closed under cartesian product and also because its groupoid cardinality is equal to 1/n.


dirichlet-series-species-Inhabited-𝔽 :
  {l1 l2 l3 : Level}  species-Inhabited-𝔽 l1 l2  UU l3 
  UU (lsuc l1  l2  l3)
dirichlet-series-species-Inhabited-𝔽 {l1} T S =
  Σ ( )
    ( λ n 
      Σ ( UU-Fin l1 (succ-ℕ n))
        ( λ F 
            ( T
              ( type-UU-Fin (succ-ℕ n) F ,
                is-finite-and-inhabited-type-UU-Fin-succ-ℕ n F)) ×
          S  cycle-prime-decomposition-ℕ (succ-ℕ n) _))

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