Natural.perm_go: def of bend-collections@1.0.0.0
Import: import bend-collections@1.0.0.0/src/math/natural.bend as Natural
Lines 125-131 of bend-collections@1.0.0.0/src/math/natural.bend: https://jend.leeeet.dev/read.txt?path=bend-collections@1.0.0.0/src/math/natural.bend&start_line=125&end_line=131

import Base

# n * (n - 1) * ... * (n - k + 1)
def perm_go(k: Nat, +m: Nat, +acc: Nat) -> Nat:
  match k:
    case 0n:
      acc
    case 1n+j:
      perm_go(j, Nat.sub(m, 1n), Nat.mul(acc, m))

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