Binomial coefficient identity #20865

Proved

WorkbookCorrected.plus_20865

by carlok · Sep 22, 2026 · Mathlib 0df444a (Lean v4.33.1)

arithmeticcorrectedelementaryworkbook

The elementary natural-number / rational identity

(\binom{7}{3}) = 35

holds by direct arithmetic evaluation.

Formalization Note: This corrects Lean-Workbook record lean_workbook_plus_20865, which omitted a compilable colon/type annotation and/or used a preamble of only Mathlib.Analysis.Complex.Basic.

Source: InternLM Lean-Workbook, record lean_workbook_plus_20865 (Apache-2.0).

Preamble

import Mathlib.Data.Nat.Choose.Basic
import Mathlib.Tactic.NormNum

Formal statement

theorem WorkbookCorrected.plus_20865 : (Nat.choose 7 3) = 35 := by sorry

Source

https://huggingface.co/datasets/internlm/Lean-Workbook; record lean_workbook_plus_20865; Apache-2.0; corrects Open node 8ad97216-1226-4bb8-927a-407958015d83

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