List.drop_append_of_le_length_sym: law of bend-mathlib@0.8.1.0
Import: import bend-mathlib@0.8.1.0/list.bend as List
Lines 2610-2618 of bend-mathlib@0.8.1.0/list.bend: https://jend.leeeet.dev/read.txt?path=bend-mathlib@0.8.1.0/list.bend&start_line=2610&end_line=2618

import Base
import bend-mathlib@0.8.1.0/nat.bend as MNat

# Dropping at most the length of the first part of an append drops only from the first part, reversed to rewrite toward the simple side.
law drop_append_of_le_length_sym:
  for -a: Quant
  for -A: Kind(a)
  for xs: List<a, A>
  for ys: List<a, A>
  for n: Nat
  for h: MNat.le(n, List.length(a, A, xs))
  {List.append(a, A, List.drop(a, A, xs, n), ys) == List.drop(a, A, List.append(a, A, xs, ys), n) : List<a, A>}

Uses (8):
  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=List.append
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.drop
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.length
  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/list.bend&name=drop_append_of_le_length
  https://jend.leeeet.dev/definition.txt?path=bend-mathlib@0.8.1.0/nat.bend&name=le