lean_workbook_plus_52895

⚠️ 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.

$\\frac{\\frac{1}{2}z+\\frac{1}{2}z+(1-z)}{3}\\ge \\sqrt[3]{\\frac{z^2(1-z)}{4}}$

Why this node was retired

The posted statement is

theorem lean_workbook_plus_52895 (z : ℝ) : (1 / 2 * z + 1 / 2 * z + (1 - z)) / 3 ≥ (z^2 * (1 - z) / 4)^(1 / 3)   :=  by sorry

A fractional-looking exponent elaborates as natural-number division (usually zero), so the formal power is not the source root.

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

Confirmed directly from the Lean text: the numeric-literal exponent carries no type ascription, so it elaborates at type ℕ where division truncates (^(1 / 3) → ^0).

Proposed corrected statement

For0≤z≤1 apply AM–GM to z/2,z/2,1−z and prove1/3≥∛(z²(1−z)/4), using the genuine nonnegative cube root.

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.