Perm.isort_by_perm: def of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/perm.bend as Perm
Lines 98-104 of bend-mathlib@0.8.1.0/perm.bend: https://jend.leeeet.dev/read.txt?path=bend-mathlib@0.8.1.0/perm.bend&start_line=98&end_line=104

import Base
import bendlib-kernel-list@1.0.0.0/list.bend as K

# Insertion sort permutes its input.
def isort_by_perm(~A: Data, ~le: A -> A -> Bool, +xs: List<&2, A>) -> K.perm(A, xs, isort_by(~A, ~le, xs)):
  match xs:
    case Nil{}:
      perm_refl(A, Nil{})
    case +x <> t:
      perm_trans(A, x <> t, x <> isort_by(~A, ~le, t), isort_by(~A, ~le, x <> t), perm_cons(A, x, t, isort_by(~A, ~le, t), isort_by_perm(~A, ~le, t)), insert_by_perm(~A, ~le, x, isort_by(~A, ~le, t)))

Uses (8):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/perm.bend&name=insert_by_perm
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/perm.bend&name=isort_by
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/perm.bend&name=perm_cons
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/perm.bend&name=perm_refl
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/perm.bend&name=perm_trans
  https://jend.leeeet.dev/definition.txt?path=bendlib-kernel-list@1.0.0.0/list.bend&name=perm