Factorial with big operators #
This file contains some lemmas on factorials in combination with big operators.
While in terms of semantics they could be in the Basic.lean
file, importing
Algebra.BigOperators.Basic
leads to a cyclic import.
theorem
Nat.descFactorial_eq_prod_range
(n : ℕ)
(k : ℕ)
:
n.descFactorial k = (Finset.range k).prod fun (i : ℕ) => n - i