The digit-sum congruence for 123

Proved

WorkbookSource.problem_32495

by wamlart · Sep 12, 2026 · Mathlib 0df444a (Lean v4.33.1)

lean-workbooksource-checked

Apply properties of $\pmod{9}$ to show that $123 \equiv 1+2+3 \pmod{9}$ .

Source: InternLM Lean-Workbook, record lean_workbook_32495 (Apache-2.0). The complete source proposition and explicit variable declarations are preserved.

Preamble

import Mathlib
open Real Nat

Formal statement

theorem WorkbookSource.problem_32495 : 123 ≡ (1 + 2 + 3) [ZMOD 9]  :=  by sorry

Source

https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, record lean_workbook_32495; Apache-2.0

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