Natural.choose: def of bend-collections-laws-crypto@1.0.0.0
Import: import bend-collections-laws-crypto@1.0.0.0/spec/math/natural.bend as Natural
Lines 67-77 of bend-collections-laws-crypto@1.0.0.0/spec/math/natural.bend: https://jend.leeeet.dev/read.txt?path=bend-collections-laws-crypto@1.0.0.0/spec/math/natural.bend&start_line=67&end_line=77

import Base

# Mathlib/Data/Nat/Choose/Basic (Pascal's rule, Nat.choose_succ_succ)
def choose(n: Nat, k: Nat) -> Nat:
  match n k:
    case 0n 0n:
      1n
    case 0n 1n+j:
      0n
    case 1n+m 0n:
      1n
    case 1n+ +m 1n+ +j:
      Nat.add(choose(m, j), choose(m, 1n+j))

Uses (2):
  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