List.perm: def of bendlib-kernel-list@1.0.0.0
Import: import bendlib-kernel-list@1.0.0.0/list.bend as List
Lines 41-43 of bendlib-kernel-list@1.0.0.0/list.bend: https://jend.leeeet.dev/read.txt?path=bendlib-kernel-list@1.0.0.0/list.bend&start_line=41&end_line=43

import Base

# Some swap derivation carries `xs` to `ys` (the existential `perm`).
def perm(-A: Data, xs: List<&2, A>, ys: List<&2, A>) -> Data:
  Sigma<&2, &2, List<&2, Nat>, s => perm_steps(A, s, xs, ys)>

Uses (4):
  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=Base/base.bend&name=Sigma
  https://jend.leeeet.dev/definition.txt?path=bendlib-kernel-list@1.0.0.0/list.bend&name=perm_steps