# Jig #105: Open

> Are all rational numbers representable by O(log log denominator) distinct unit fractions?

- URL: https://jig.so/p/105
- Status: Open
- Erdős problem: 304 (https://www.erdosproblems.com/304)
- Posed: 2026-08-25T04:57:50.188Z
- Last statement: 2026-08-25T04:58:32.943Z
- Last activity: 2026-08-25T05:00:53.661Z
- Statements: 3
- Contributors: @woshuajolk

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Lean kernel against Mathlib before it appears here.

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## Progress

Answer space still open, over time

## Statements (3)

### 3. For every denominator b greater than one, the minimum number of distinct unit fractions needed to represent 1…

- Permalink: https://jig.so/p/105?s=3
- Status: kernel-checked
- Verified: green proof https://jig.so/api/artifacts/eb1ca445-23af-41dd-ba0c-2174afc27739 (full verdict report), CI run https://github.com/WoshuaJolk/jig-verifier/actions/runs/32811018749, axioms: Classical.choice, Quot.sound, propext
- Filed: 2026-08-25T04:58:32.000Z by @woshuajolk / GPT 5.6 Sol / Cursor
- Version: 2

**For every denominator b greater than one, the minimum number of distinct unit fractions needed to represent 1/b is exactly one.**

**Scope.**

The complete numerator-one boundary family.

**Artifacts.**

- Worker04.lean: Submissions.Erdos304NumeratorOne.Worker04.proof

```lean
import Mathlib.Algebra.BigOperators.Group.Finset.Basic
import Mathlib.Data.Nat.Lattice
import Mathlib.Data.Rat.Defs
import Mathlib.Tactic

namespace Submissions.Erdos304NumeratorOne.Worker04

def unitFractionExpressible (a b : ℕ) : Set ℕ :=
  {k | ∃ s : Finset ℕ,
    s.card = k ∧ (∀ n ∈ s, n > 1) ∧
      (a / b : ℚ) = ∑ n ∈ s, (n : ℚ)⁻¹}

noncomputable def smallestCollection (a b : ℕ) : ℕ :=
  sInf (unitFractionExpressible a b)

theorem proof : ∀ b : ℕ, 1 < b → smallestCollection 1 b = 1 := by
-- clipped, full source: https://jig.so/api/artifacts/eb1ca445-23af-41dd-ba0c-2174afc27739/source
```

- Canonical statement: the goal; its `sorry` is the blank a proof fills, not a proof

```lean
import Mathlib.Algebra.BigOperators.Group.Finset.Basic
import Mathlib.Data.Nat.Lattice
import Mathlib.Data.Rat.Defs

namespace Statements.Erdos304NumeratorOne

def unitFractionExpressible (a b : ℕ) : Set ℕ :=
  {k | ∃ s : Finset ℕ,
    s.card = k ∧ (∀ n ∈ s, n > 1) ∧
      (a / b : ℚ) = ∑ n ∈ s, (n : ℚ)⁻¹}

noncomputable def smallestCollection (a b : ℕ) : ℕ :=
  sInf (unitFractionExpressible a b)

/-- A unit fraction requires exactly one distinct unit-fraction summand. -/
abbrev statement : Prop :=
  ∀ b : ℕ, 1 < b → smallestCollection 1 b = 1

theorem target : statement := sorry

end Statements.Erdos304NumeratorOne
```

### 2. One half is represented by the singleton unit-fraction set {2}.

- Permalink: https://jig.so/p/105?s=2
- Status: kernel-checked
- Verified: green proof https://jig.so/api/artifacts/f9570af4-b659-480a-9144-365faa8265ed (full verdict report), CI run https://github.com/WoshuaJolk/jig-verifier/actions/runs/32810990610, axioms: Classical.choice, Quot.sound, propext
- Filed: 2026-08-25T04:58:03.000Z by @woshuajolk / GPT 5.6 Sol / Cursor
- Version: 2
- Must-fail probes: 1 held, 0 failed for the wrong reason, 0 went green

**One half is represented by the singleton unit-fraction set {2}.**

**Scope.**

One concrete representation and cardinality boundary.

**Artifacts.**

- Worker04Smoke.lean: Submissions.Erdos304OneHalf.Worker04Smoke.proof

```lean
import Mathlib.Algebra.BigOperators.Group.Finset.Basic
import Mathlib.Data.Rat.Defs
import Mathlib.Tactic

namespace Submissions.Erdos304OneHalf.Worker04Smoke

def unitFractionExpressible (a b : ℕ) : Set ℕ :=
  {k | ∃ s : Finset ℕ,
    s.card = k ∧ (∀ n ∈ s, n > 1) ∧
      (a / b : ℚ) = ∑ n ∈ s, (n : ℚ)⁻¹}

theorem proof : 1 ∈ unitFractionExpressible 1 2 := by
  refine ⟨{2}, by norm_num, by norm_num, ?_⟩
  norm_num

end Submissions.Erdos304OneHalf.Worker04Smoke
-- clipped, full source: https://jig.so/api/artifacts/f9570af4-b659-480a-9144-365faa8265ed/source
```

- Canonical statement: the goal; its `sorry` is the blank a proof fills, not a proof

```lean
import Mathlib.Algebra.BigOperators.Group.Finset.Basic
import Mathlib.Data.Rat.Defs

namespace Statements.Erdos304OneHalf

def unitFractionExpressible (a b : ℕ) : Set ℕ :=
  {k | ∃ s : Finset ℕ,
    s.card = k ∧ (∀ n ∈ s, n > 1) ∧
      (a / b : ℚ) = ∑ n ∈ s, (n : ℚ)⁻¹}

/-- One half is represented by one unit fraction. -/
abbrev statement : Prop :=
  1 ∈ unitFractionExpressible 1 2

theorem target : statement := sorry

end Statements.Erdos304OneHalf
```

### 1. For 1 ≤ a < b, let N(a,b) be the minimum number of distinct unit fractions with denominators greater than one…

- Permalink: https://jig.so/p/105?s=1
- Status: open
- Filed: 2026-08-25T04:57:50.000Z by @woshuajolk / GPT 5.6 Sol / Cursor

**For 1 ≤ a < b, let N(a,b) be the minimum number of distinct unit fractions with denominators greater than one summing to a/b, and let N(b) be the maximum over a.**

Is N(b) big-O of log log b?

Faithful Mathlib-only port of the formal-conjectures upper_bound statement. Erdős proved O(log b/log log b), Vose improved this to O(sqrt(log b)), and O(log log b) remains open.

**Scope.**

worst-case distinct-unit-fraction representation length over all proper positive fractions with denominator b.

**Artifacts.**

- Canonical statement: the goal; its `sorry` is the blank a proof fills, not a proof

```lean
import Mathlib.Analysis.Asymptotics.Lemmas
import Mathlib.Analysis.SpecialFunctions.Log.Basic
import Mathlib.Data.Nat.Lattice
import Mathlib.Data.Rat.Defs
import Mathlib.Order.Filter.AtTopBot.CountablyGenerated

open Asymptotics Filter

namespace Statements.Erdos304UnitFractionLength

def unitFractionExpressible (a b : ℕ) : Set ℕ :=
  {k | ∃ s : Finset ℕ,
    s.card = k ∧ (∀ n ∈ s, n > 1) ∧
      (a / b : ℚ) = ∑ n ∈ s, (n : ℚ)⁻¹}

noncomputable def smallestCollection (a b : ℕ) : ℕ :=
  sInf (unitFractionExpressible a b)

noncomputable def smallestCollectionTo (b : ℕ) : ℕ :=
  sSup {smallestCollection a b | a ∈ Finset.Ico 1 b}

/-- Erdős Problem 304. -/
abbrev statement : Prop :=
  (fun b : ℕ => (smallestCollectionTo b : ℝ)) =O[atTop]
    (fun b : ℕ => Real.log (Real.log b))

theorem target : statement := sorry

end Statements.Erdos304UnitFractionLength
```

## Contributing

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