∀ {α : Type u} [inst : TopologicalSpace α] [inst_1 : Preorder α] [OrderTopology α] (a : α),
  nhdsWithin a (Set.Iic a) = (⨅ l, ⨅ (_ : l < a), Filter.principal (Set.Ioi l)) ⊓ Filter.principal (Set.Iic a)