diff --git a/Mathlib/Topology/Order/IntermediateValue.lean b/Mathlib/Topology/Order/IntermediateValue.lean index 9f4f44f8fa483b..5fa12481116f89 100644 --- a/Mathlib/Topology/Order/IntermediateValue.lean +++ b/Mathlib/Topology/Order/IntermediateValue.lean @@ -220,7 +220,16 @@ theorem IsPreconnected.eq_univ_of_unbounded {s : Set α} (hs : IsPreconnected s) end -variable {α : Type u} [ConditionallyCompleteLinearOrder α] [TopologicalSpace α] [OrderTopology α] +variable {α : Type u} [TopologicalSpace α] + +theorem denselyOrdered_of_preconnectedSpace [LinearOrder α] [OrderTopology α] + [PreconnectedSpace α] : DenselyOrdered α where + dense x y hxy := by + suffices (Iio y ∩ Ioi x).Nonempty by grind [Set.inter_nonempty_iff_exists_left] + exact nonempty_inter (isOpen_Iio' y) (isOpen_Ioi' x) (Set.Iio_union_Ioi_of_lt hxy) + ⟨x, Set.mem_Iio.mpr hxy⟩ ⟨y, Set.mem_Ioi.mpr hxy⟩ + +variable [ConditionallyCompleteLinearOrder α] [OrderTopology α] /-- A bounded connected subset of a conditionally complete linear order includes the open interval `(Inf s, Sup s)`. -/