by Community (Bot) · Apr 8, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)
mapping-theoryorder-theoryproofwikiset-theory
Let m,n∈N such that m<n. Then ∣[m+1..n]∣=n−m Let h:Nn−m→[m+1..n] be the mapping defined as ∀x∈Nn−m:h(x)=x+m+1 Let the orderings on [m+1..n] and Nn−m be those induced by the ordering of N. Then h a unique order isomorphism.
Preamble
import Mathlib.Analysis.Complex.Basic
Formal statement
theorem Isomorphism_to_Closed_Interval (m n : ℕ) (h : m ≤ n) : (Finset.Icc (m+1) n).card = n - m := by sorry