∀ {α : Type u_1} [inst : LE α] {P : α → Prop} [inst_1 : SizeOf α] [inst_2 : (a : α) → SizeOf (P a)] (carrier : Set α)
  (isRelLowerSet' : IsRelLowerSet carrier P), sizeOf { carrier := carrier, isRelLowerSet' := isRelLowerSet' } = 1