def Perm.self
import bend-collections-laws-crypto@1.0.0.0/spec/math/natural.bend as Naturalimport Base
import bend-collections-laws-crypto@1.0.0.0/src/math/natural.bend as M
188def Perm.self(+n: Nat) -> Type:
189 {M.perm(n, n) == factorial(n) : Nat}