Perm.merge_by_perm_nat: def of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/perm.bend as Perm
Lines 157-159 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=157&end_line=159

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

# Merging two Nat lists permutes their concatenation.
def merge_by_perm_nat(+xs: List<&2, Nat>, +ys: List<&2, Nat>) -> K.perm(Nat, List.append(&2, Nat, xs, ys), merge_by(~Nat, ~Nat.is_le, xs, ys)):
  merge_by_perm(~Nat, ~Nat.is_le, xs, ys)

Uses (7):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.append
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.is_le
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/perm.bend&name=merge_by
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/perm.bend&name=merge_by_perm
  https://jend.leeeet.dev/definition.txt?path=bendlib-kernel-list@1.0.0.0/list.bend&name=perm