∀ {ι : Type u_1} {μ : Type u_2} [inst : DecidableEq ι] [inst_1 : AddCommMonoid μ] [inst_2 : PartialOrder μ]
  [CanonicallyOrderedAdd μ] [inst_4 : Finset.HasAntidiagonal μ] [inst_5 : DecidableEq μ] (s : Finset ι),
  s.piAntidiag 0 = {0}