leanprover / leanprover/lean4

`omega` failing due to powers of numerals

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Description

Prerequisites

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Description

The following example fails:

example (n : Nat) : 0 ≤ 2 ^ n := by 
  omega

with the message:

omega could not prove the goal:
a possible counterexample may satisfy the constraints
  a ≤ -1
where
 a := ↑2 ^ n

At the same time, the following more general example works:

example (m n : Nat) : 0 ≤ m ^ n := by 
  omega
Context

Related discussion in Zulip: #lean4 > Omega failing due to terms with power?

Steps to Reproduce

Run the code above.

Expected behavior: omega closes the goal above.

Actual behavior: omega fails to close the goal.

Versions

4.22.0-rc3
4.23.0-nightly-2025-07-04

Impact

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Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running the minimal omega examples from the issue and compare the failing numeral-base power case with the working general case. Trace the omega implementation from its tactic entry point; done means the first example is closed while the existing general case continues to work.

Written by the indexing model from the issue text.

Assessment

Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Clearly specified
Newbie friendliness
45/100

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