lean_workbook_plus_61512

⚠️ Retired — specification defect

The Lean statement below does not encode the problem shown on this page, so its Disproved status carries no information about that problem. Do not import this node or use it as a dependency.

Case 2: $f(-1)=1, f(0)=0, f(1)=-1$

Why this node was retired

The posted statement is

theorem lean_workbook_plus_61512 (f : ℤ → ℤ) (hf : f (-1) = 1 ∧ f 0 = 0 ∧ f 1 = -1) : ∀ x, f x = x   :=  by sorry

The conclusion f=id contradicts even the stated value f(1)=−1; three values cannot classify a general function.

The recorded counterexample refutes the statement as encoded. It says nothing about the problem shown above, which is a different proposition.

Proposed corrected statement

Recover the original functional equation before extending the case values to any global formula; f(x)=−x is one compatible example, not a unique consequence of the three values.

Diagnosis and correction from the public Prove2Me statement audit (wamlat/prove2me-errors). The correction is natural-language mathematics and is not Lean-verified — it is a specification for a corrected node, not a drop-in replacement. No corrected replacement node exists yet.