Blist.pre_len: def of bend-collections-laws-crypto@1.0.0.0
Import: import bend-collections-laws-crypto@1.0.0.0/proofs/crypto/secp256k1/blist.bend as Blist
Lines 61-68 of bend-collections-laws-crypto@1.0.0.0/proofs/crypto/secp256k1/blist.bend: https://jend.leeeet.dev/read.txt?path=bend-collections-laws-crypto@1.0.0.0/proofs/crypto/secp256k1/blist.bend&start_line=61&end_line=68

import Base
import bend-collections-laws-crypto@1.0.0.0/spec/crypto/secp256k1/curve.bend as CV
import bend-collections-laws-crypto@1.0.0.0/src/crypto/secp256k1/bytes.bend as B
import bend-collections-laws-crypto@1.0.0.0/proofs/lib/logic.bend as Lg

def pre_len(a: Nat, +b: Nat, xs: List<&2, U32>, +h: {B.has_len(Nat.add(a, b), xs) == True{} : Bool}) -> {B.has_len(a, CV.first(a, xs)) == True{} : Bool}:
  match a xs:
    case 0n _:
      {==}
    case 1n+k Nil{}:
      Empty.absurd({B.has_len(1n+k, CV.first(1n+k, [])) == True{} : Bool}, Lg.false_true(h))
    case 1n+k x <> t:
      pre_len(k, b, t, h)

Uses (9):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Empty.absurd
  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=Nat.add
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/proofs/lib/logic.bend&name=false_true
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/spec/crypto/secp256k1/curve.bend&name=first
  https://jend.leeeet.dev/definition.txt?path=bend-collections-laws-crypto@1.0.0.0/src/crypto/secp256k1/bytes.bend&name=has_len