A triple evaluation of a linear recurrence

Proved

WorkbookSource.problem_29531

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

lean-workbooksource-checked

Find $f(f(f(5)))$ given $f(x) = f(x-1) + 4$ and $f(0) = 3$ .

Source: InternLM Lean-Workbook, record lean_workbook_29531 (Apache-2.0). The complete source proposition and its explicit variable declarations are preserved.

Preamble

import Mathlib
open Real Nat

Formal statement

theorem WorkbookSource.problem_29531 (f : ℤ → ℤ) (h₁ : ∀ x, f x = f (x - 1) + 4) (h₂ : f 0 = 3) : f (f (f 5)) = 383  :=  by sorry

Source

https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, record lean_workbook_29531; Apache-2.0

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