Natural.desc: 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 59-65 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=59&end_line=65

import Base

# n.descFactorial k: (n - k) * n.descFactorial k at k + 1
def desc(+n: Nat, k: Nat) -> Nat:
  match k:
    case 0n:
      1n
    case 1n+ +j:
      Nat.mul(Nat.sub(n, j), desc(n, j))

Uses (3):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.mul
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.sub