lean_workbook_plus_72103

⚠️ Retired — specification defect

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

Prove that among $5$ natural numbers, one can always pick three such that their sum is divisible by $3$

Why this node was retired

The posted statement is

theorem lean_workbook_plus_72103 (A: Finset ℕ) (hA: A.card >= 5) : ∃ x y z: ℕ, x ∈ A ∧ y ∈ A ∧ z ∈ A ∧ (x + y + z) % 3 = 0   :=  by sorry

The three selected elements need not be distinct.

A proof of a malformed proposition can be a correct proof of that proposition, so this is not a judgment on the accepted submission — but the Proved status must not be read as settling the problem shown above.

Proposed corrected statement

Require x,y,z to be pairwise distinct elements of A in the conclusion.

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.