Prove2Me

Factorial arithmetic identity #79983

Disproved
WorkbookCorrected.plus_79983

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

arithmeticcorrectedelementaryworkbook

The elementary natural-number / rational identity

8!/(2!4)=908! / (2!^4) = 90

holds by direct arithmetic evaluation.

Formalization Note: This corrects Lean-Workbook record lean_workbook_plus_79983, 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_79983 (Apache-2.0).

Preamble
import Mathlib.Data.Nat.Factorial.Basic
import Mathlib.Tactic.NormNum
Formal statement
theorem WorkbookCorrected.plus_79983 : (Nat.factorial 8) / ((Nat.factorial 2)^4) = 90 := by sorry
Source
https://huggingface.co/datasets/internlm/Lean-Workbook; record lean_workbook_plus_79983; Apache-2.0; corrects Open node 7c1824f7-b6b1-4fa1-8fee-f4051b38d3c9

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