LAWS.ends_join: law of lawful-fields@0.1.1.0
Import: import lawful-fields@0.1.1.0/LAWS.bend as LAWS
Lines 154-161 of lawful-fields@0.1.1.0/LAWS.bend: https://jend.leeeet.dev/read.txt?path=lawful-fields@0.1.1.0/LAWS.bend&start_line=154&end_line=161

import Base
import lawful-fields@0.1.1.0/defs.bend as F

# Piece k ends at the k-th end: the first k+1 pieces joined, from from.
law ends_join:
  for ps: List<&2, List<&2, U32>>
  for sep: U32
  for from: Nat
  for k: Nat
  for h: {Nat.is_lt(k, List.length(&2, List<&2, U32>, ps)) == True{} : Bool}
  {List.get(&2, Nat, F.ends(ps, from), k) == Some{Nat.add(from, List.length(&2, U32, F.join(List.take(&2, List<&2, U32>, ps, Nat.add(k, 1n)), sep)))} : Maybe<&2, Nat>}

Uses (13):
  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=Base/base.bend&name=List.get
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.length
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.take
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Maybe
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.add
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.is_lt
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32
  https://jend.leeeet.dev/definition.txt?path=lawful-fields@0.1.1.0/defs.bend&name=ends
  https://jend.leeeet.dev/definition.txt?path=lawful-fields@0.1.1.0/defs.bend&name=join
  https://jend.leeeet.dev/definition.txt?path=lawful-fields@0.1.1.0/proof_list.bend&name=ends_join