Intervals #
In any preorder, we define intervals (which on each side can be either infinite, open or closed) using the following naming conventions:
i: infiniteo: openc: closed
Each interval has the name I + letter for left side + letter for right side.
For instance, Ioc a b denotes the interval (a, b].
The definitions can be found in Mathlib/Order/Interval/Set/Defs.lean.
This file contains basic facts on inclusion of and set operations on intervals
(where the precise statements depend on the order's properties;
statements requiring LinearOrder are in Mathlib/Order/Interval/Set/LinearOrder.lean).
A conscious decision was made not to list all possible inclusion relations. Monotonicity results and "self" results are included. Most use cases can suffice with a transitive combination of those, for example:
theorem Ico_subset_Ici (h : a₂ ≤ a₁) : Ico a₁ b₁ ⊆ Ici a₂ :=
(Ico_subset_Ico_left h).trans Ico_subset_Ici_self
Logical equivalences, such as Icc_subset_Ici_iff, are however stated.
Alias of Set.self_mem_Ici.
Alias of Set.self_mem_Iic.
In an order without maximal elements, the intervals Ioi are nonempty.
In an order without minimal elements, the intervals Iio are nonempty.
Alias of the reverse direction of Set.Ici_subset_Ici.
Alias of the reverse direction of Set.Ici_ssubset_Ici.
Alias of the reverse direction of Set.Iic_subset_Iic.
Alias of the reverse direction of Set.Iic_ssubset_Iic.
Alias of the reverse direction of Set.Ioi_eq_empty_iff.
Alias of the reverse direction of Set.Iio_eq_empty_iff.