Perm.internal_swap_at_invol: def of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/perm.bend as Perm
Lines 267-277 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=267&end_line=277

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

def internal_swap_at_invol(-A: Data, +i: Nat, +xs: List<&2, A>) -> {K.swap_at(A, i, K.swap_at(A, i, xs)) == xs : List<&2, A>}:
  match i:
    case 0n:
      internal_swap_head_invol(A, xs)
    case 1n+p:
      match xs:
        case Nil{}:
          {==}
        case +x <> t:
          %Equal.sym(List<&2, A>, K.swap_at(A, p, K.swap_at(A, p, t)), t, internal_swap_at_invol(A, p, t)) : {x <> _ == x <> t : List<&2, A>}
          {==}

Uses (5):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Equal.sym
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/perm.bend&name=internal_swap_head_invol
  https://jend.leeeet.dev/definition.txt?path=bendlib-kernel-list@1.0.0.0/list.bend&name=swap_at