law join_at

lawful-fields@0.1.1.0 · proof_list.bend:320

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

320law join_at:
321  for +ps: List<&2, List<&2, U32>>
322  for +sep: U32
323  for +k: Nat
324  for +h: {Nat.is_lt(Nat.add(k, 1n), List.length(&2, List<&2, U32>, ps)) == True{} : Bool}
325  {F.join(ps, sep) == List.append(&2, U32, F.join(List.take(&2, List<&2, U32>, ps, Nat.add(k, 1n)), sep), Con{sep, F.join(List.drop(&2, List<&2, U32>, ps, Nat.add(k, 1n)), sep)}) : List<&2, U32>}