∀ {α : Type u} [inst : DecidableEq α] {β : Type v} [inst_1 : Fintype α] [inst_2 : DecidableEq β] [inst_3 : Fintype β]
  (σa : Equiv.Perm α) (σb : Equiv.Perm β), Equiv.Perm.sign (σa.sumCongr σb) = Equiv.Perm.sign σa * Equiv.Perm.sign σb