The lonely runner conjecture
Runners at distinct speeds on a circular track: is each of them, at some moment, far from all the others?
▸Motivation
Wills 1967, Cusick 1973, named by Goddyn in 1998. Proved for up to seven runners; open for eight.
The combinatorial statement is equivalent to a question about view-obstruction in geometry and to one about chromatic numbers of distance graphs, which is unusual — three unrelated-looking areas stuck at the same place.
Wills 1967; Cusick 1973; named by Goddyn 1998. Known for n ≤ 7.
▸Lean API
import Mathlib.Data.Finset.Card
import Mathlib.Data.Rat.Defs
import Mathlib.Algebra.Order.Ring.Rat
namespace Conjectura.CB005
/-- Runners with distinct constant speeds start together on a circular track of
circumference one. Is every runner, at some moment, at distance at least `1/n` from
all the others? Proved for up to seven runners. -/
def goal : Prop :=
∀ (n : ℕ) (v : Fin n → ℚ), 0 < n → Function.Injective v →
∀ i : Fin n, ∃ t : ℚ, ∀ j : Fin n, j ≠ i →
∃ k : ℤ, 1 / (n : ℚ) ≤ |(v i - v j) * t - (k : ℚ)|
end Conjectura.CB005▸Definition1
- InjectiveFunction.Injective
class
▸Related work0
▸For your AI
I am proving a theorem in Lean 4 and submitting it to Conjectura.
## Problem CB005 — The lonely runner conjecture
Runners at distinct speeds on a circular track: is each of them, at some moment, far from all the others?
## Environment (fixed — do not assume anything newer)
- Lean toolchain: `leanprover/lean4:v4.33.0-rc1`
- Mathlib: `v4.33.0-rc1`
If a lemma you want does not exist in that Mathlib, prove it inline instead of
importing something newer.
## The exact statement I must prove
```lean
theorem solution : ∀ (n : ℕ) (v : Fin n → ℚ), 0 < n → Function.Injective v →
∀ i : Fin n, ∃ t : ℚ, ∀ j : Fin n, j ≠ i → ∃ k : ℤ, 1 / (n : ℚ) ≤ |(v i - v j) * t - k| := by
sorry
```
## The file I submit
```lean
import Conjectura.Problems.CB005.Statement
namespace Submission
theorem solution : Conjectura.CB005.goal := by
sorry
end Submission
```
## The Lean definitions of every term in this problem
These are the actual definitions your proof will be checked against. Do not
substitute your own version of any of them.
### Injective
class
```lean
Function.Injective
```
Defined in Mathlib.
## Rules — submissions violating these are rejected automatically
1. **Do not change the name or type of `solution`.** It must satisfy the
statement above exactly.
2. **Do not redefine or shadow anything from the problem's Statement module.**
Declaring your own `goal`, or redefining a name it depends on, produces a
proof of a *different* statement and is rejected. This is the single most
common rejection.
3. **No `sorry`** anywhere, including in helper lemmas. It surfaces as the
axiom `sorryAx` and is detected transitively through imports.
4. **No `native_decide`** — it surfaces as `Lean.ofReduceBool` and is not
accepted, because it trusts compiled code rather than the kernel.
5. Only these axioms are permitted: `propext`, `Classical.choice`,
`Quot.sound`.
6. Follow Mathlib style: hypotheses left of the colon, explicit types,
`snake_case` theorem names, `UpperCamelCase` types.
## What I want from you
Here is my argument in informal mathematics:
> [PASTE YOUR PROOF SKETCH HERE]
Turn it into Lean 4 that compiles under the environment above and satisfies the
statement exactly. Where you are unsure a lemma exists in this Mathlib version,
say so explicitly rather than guessing a name.Submissions are not open yet
Conjectura is in beta. You can read every statement, every definition and the Lean behind them, and download the exact files the checker uses — but proofs are not being accepted yet.
The reason is a deliberate order of operations. Accepting a proof means running a stranger’s code and standing behind a verdict, and no statement here yet carries a researcher’s name. A machine-checked answer to a question nobody has vouched for is worth very little, so the vouching comes first.
The English write-ups are also switched off during the beta. Nothing on this page is generated by a model.
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