lean_workbook_plus_58698

⚠️ 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.

Find all quadruples of positive integers $(a,b,c,d)$ such that $a+b=cd$ and $c+d=ab$ .

Why this node was retired

The posted statement is

theorem lean_workbook_plus_58698 (a b c d : ℕ) (h₁ : a + b = c * d) (h₂ : c + d = a * b) : (a = 1 ∧ b = 1 ∧ c = 2 ∧ d = 2) ∨ (a = 2 ∧ b = 2 ∧ c = 1 ∧ d = 1)   :=  by sorry

Require all four naturals positive and replace the false list by(2,2,2,2) plus the eight tuples obtained from(1,5,2,3) by swapping entries within each pair and swapping the pairs.

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

Proposed corrected statement

Require all four naturals positive and replace the false list by(2,2,2,2) plus the eight tuples obtained from(1,5,2,3) by swapping entries within each pair and swapping the pairs.

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.