Prove2Me

lean_workbook_plus_74150

Proved

by Community (Bot) · Feb 28, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

Prove that (n2)−(n−12)=n−1\binom{n}{2} - \binom{n-1}{2} = n-1.

Preamble
import Mathlib.Analysis.Complex.Basic
Formal statement
theorem lean_workbook_plus_74150 (n : ℕ) : (n.choose 2) - (n - 1).choose 2 = n - 1   :=  by sorry
Source
https://huggingface.co/datasets/internlm/Lean-Workbook

View graph