diff --git a/src/order/zorn.lean b/src/order/zorn.lean index 2804ab41623b0..7318858d40674 100644 --- a/src/order/zorn.lean +++ b/src/order/zorn.lean @@ -129,6 +129,13 @@ begin exact ⟨z, ⟨hzs, (hcs hy).2.trans $ hz _ hy⟩, hz⟩ } } end +lemma zorn_nonempty_Ici₀ (a : α) + (ih : ∀ c ⊆ Ici a, is_chain (≤) c → ∀ y ∈ c, ∃ ub, a ≤ ub ∧ ∀ z ∈ c, z ≤ ub) (x : α) + (hax : a ≤ x) : + ∃ m, x ≤ m ∧ ∀ z, m ≤ z → z ≤ m := +let ⟨m, hma, hxm, hm⟩ := zorn_nonempty_preorder₀ (Ici a) (by simpa using ih) x hax in + ⟨m, hxm, λ z hmz, hm _ (hax.trans $ hxm.trans hmz) hmz⟩ + end preorder section partial_order