lean_workbook_plus_13952

⚠️ 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.

Given $0<a , b , c , d<1$ and $2(1-a)(1-b) = 2 + 2ab - 2a -2b = a^{2} + b^{2} + c^{2} + d^{2} +2ab -2a -2b +1 = (a+b -1 )^{2} + c^{2} + d^{2} \geq c^{2} + d^{2} \geq 2cd$ Deduce $(1-a)(1-b) \geq cd$

Why this node was retired

The posted statement is

theorem lean_workbook_plus_13952 : ∀ a b c d : ℝ, a ∈ Set.Ioo 0 1 ∧ b ∈ Set.Ioo 0 1 ∧ c ∈ Set.Ioo 0 1 ∧ d ∈ Set.Ioo 0 1 → (1 - a) * (1 - b) ≥ c * d   :=  by sorry

Restore a²+b²+c²+d²=1, which is required by the equality chain in the source, retaining the interval hypotheses.

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

Proposed corrected statement

Restore a²+b²+c²+d²=1, which is required by the equality chain in the source, retaining the interval hypotheses.

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.