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chore: Add doc strings

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jstoobysmith 2024-10-19 10:07:03 +00:00
parent 1f3ba14462
commit 48bec8c891
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HepLean/Mathematics/Fin.lean
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@ -21,6 +21,8 @@ namespace HepLean.Fin
open Fin
variable {n : Nat}
/-- Given a `i` and `x` in `Fin n.succ.succ` returns an element of `Fin n.succ`
subtracting 1 if `i.val ≤ x.val` else casting x. -/
def predAboveI (i x : Fin n.succ.succ) : Fin n.succ :=
if h : x.val < i.val then
⟨x.val, by omega⟩
@ -245,6 +247,8 @@ lemma finExtractOne_symm_inl_apply {n : ℕ} (i : Fin n.succ) :
ext
rfl
/-- Given an equivalence `Fin n.succ.succ ≃ Fin n.succ.succ`, and an `i : Fin n.succ.succ`,
the map `Fin n.succ → Fin n.succ` obtained by dropping `i` and it's image. -/
def finExtractOnPermHom (i : Fin n.succ.succ) (σ : Fin n.succ.succ ≃ Fin n.succ.succ) :
Fin n.succ → Fin n.succ := fun x => predAboveI (σ i) (σ ((finExtractOne i).symm (Sum.inr x)))