PROOF.pk.at: def of bend-osdev-pkcs7@0.1.0.0
Import: import bend-osdev-pkcs7@0.1.0.0/PROOF.bend as PROOF
Lines 1322-1330 of bend-osdev-pkcs7@0.1.0.0/PROOF.bend: https://jend.leeeet.dev/read.txt?path=bend-osdev-pkcs7@0.1.0.0/PROOF.bend&start_line=1322&end_line=1330

import Base
import bend-osdev-bytes@0.1.1.0/bytes.bend as B
import bend-osdev-bytes@0.1.1.0/LAWS.bend as BL
import bend-osdev-pkcs7@0.1.0.0/pkcs7.bend as P

# its last byte, at L + p1 of m and it
def pk.at(+m: B.Octets, +p1: Nat) -> {B.Octets.at(B.Octets.append(m, pk.pad(p1)), Nat.add(B.Octets.len(m), p1)) == Some{B.byte(U32.from_nat(1n+p1))} : Maybe<&2, U32>}:
  %Equal.sym(Maybe<&2, U32>, B.Octets.at(B.Octets.append(m, pk.pad(p1)), Nat.add(B.Octets.len(m), p1)), B.Octets.at(pk.pad(p1), p1), BL.octets_at_append_add(m, pk.pad(p1), p1)) : {_ == Some{B.byte(U32.from_nat(1n+p1))} : Maybe<&2, U32>}
  %Equal.sym(Maybe<&2, U32>, B.Octets.at(pk.pad(p1), p1), B.at(B.Octets.to_list(pk.pad(p1)), p1), BL.octets_at_list(pk.pad(p1), p1)) : {_ == Some{B.byte(U32.from_nat(1n+p1))} : Maybe<&2, U32>}
  %Equal.sym(List<&2, U32>, B.Octets.to_list(pk.pad(p1)), B.mask(P.pkcs7.fill(1n+p1, U32.from_nat(1n+p1))), BL.octets_to_of(P.pkcs7.fill(1n+p1, U32.from_nat(1n+p1)))) : {B.at(_, p1) == Some{B.byte(U32.from_nat(1n+p1))} : Maybe<&2, U32>}
  %Equal.sym(List<&2, U32>, B.mask(P.pkcs7.fill(1n+p1, U32.from_nat(1n+p1))), P.pkcs7.fill(1n+p1, B.byte(U32.from_nat(1n+p1))), pk.mask_fill(1n+p1, U32.from_nat(1n+p1))) : {B.at(_, p1) == Some{B.byte(U32.from_nat(1n+p1))} : Maybe<&2, U32>}
  %Equal.sym(List<&2, U32>, B.drop(p1, P.pkcs7.fill(1n+p1, B.byte(U32.from_nat(1n+p1)))), Con{B.byte(U32.from_nat(1n+p1)), Nil{}}, pk.drop_fill(p1, B.byte(U32.from_nat(1n+p1)))) : {B.at.head(_) == Some{B.byte(U32.from_nat(1n+p1))} : Maybe<&2, U32>}
  %pk.bb(U32.from_nat(1n+p1)) : {Some{B.byte(B.byte(U32.from_nat(1n+p1)))} == Some{_} : Maybe<&2, U32>}
  {==}

Uses (25):
  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=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=U32
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=U32.from_nat
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-bytes@0.1.1.0/LAWS.bend&name=octets_at_append_add
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-bytes@0.1.1.0/LAWS.bend&name=octets_at_list
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-bytes@0.1.1.0/LAWS.bend&name=octets_to_of
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-bytes@0.1.1.0/bytes.bend&name=Octets
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-bytes@0.1.1.0/bytes.bend&name=Octets.append
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-bytes@0.1.1.0/bytes.bend&name=Octets.at
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-bytes@0.1.1.0/bytes.bend&name=Octets.len
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-bytes@0.1.1.0/bytes.bend&name=Octets.to_list
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-bytes@0.1.1.0/bytes.bend&name=at
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-bytes@0.1.1.0/bytes.bend&name=at.head
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-bytes@0.1.1.0/bytes.bend&name=byte
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-bytes@0.1.1.0/bytes.bend&name=drop
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-bytes@0.1.1.0/bytes.bend&name=mask
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-pkcs7@0.1.0.0/PROOF.bend&name=pk.bb
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-pkcs7@0.1.0.0/PROOF.bend&name=pk.drop_fill
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-pkcs7@0.1.0.0/PROOF.bend&name=pk.mask_fill
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-pkcs7@0.1.0.0/PROOF.bend&name=pk.pad
  https://jend.leeeet.dev/definition.txt?path=bend-osdev-pkcs7@0.1.0.0/pkcs7.bend&name=pkcs7.fill