law is_empty_iff_length_eq_zero_sym

bend-mathlib@0.8.1.0 · list.bend:3003

import Base

3003# A list is empty exactly when its length is zero, reversed to rewrite toward the simple side.
3004law is_empty_iff_length_eq_zero_sym:
3005  for -a: Quant
3006  for -A: Kind(a)
3007  for xs: List<a, A>
3008  {Nat.is_eq(List.length(a, A, xs), 0n) == List.is_empty(a, A, xs) : Bool}