Prove2Me

Binomial coefficient identity #33342

Proved
WorkbookCorrected.plus_33342

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

arithmeticcorrectedelementaryworkbook

The elementary natural-number / rational identity

((123))/2=110(\binom{12}{3})/2 = 110

holds by direct arithmetic evaluation.

Formalization Note: This corrects Lean-Workbook record lean_workbook_plus_33342, 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_33342 (Apache-2.0).

Preamble
import Mathlib.Data.Nat.Choose.Basic
import Mathlib.Tactic.NormNum
Formal statement
theorem WorkbookCorrected.plus_33342 : (Nat.choose 12 3) / 2 = 110 := by sorry
Source
https://huggingface.co/datasets/internlm/Lean-Workbook; record lean_workbook_plus_33342; Apache-2.0; corrects Open node 91b602fe-4286-4a68-890b-c6d7b91c7dc0

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