Language Tactics Playground Academy Problems Pricing

All problemsProblems LeaderboardRanking My progressProgress

Courses →Get thePass · €10

18. Reversing twice

HardVerified programAcademy Pass

An accumulator-based reverse is its own inverse.

lists induction generalization

Opening the problem…

Similar problems

12. Verified maximum Medium
36. Verified membership test Easy
23. Sum over an append Easy
19. Insertion sort sorts Hard

← 17. Sum of odd numbers 19. Insertion sort sorts →

A comprehensive learning platform for the Lean 4 programming language and theorem prover.

Lean 4 on GitHub

Learn

Language Guide
Tactics Reference
Lean Playground
Interactive Academy
Lean Problems
Proof Stories
Pricing

Community

Community Forum
Lean Zulip
Official Lean Website
Mathlib Documentation

Site

About
Contact
Editorial Policy
Your Account

Policies

Privacy Policy
Terms of Use
Withdraw from contract
Legal Notice

Built for the Lean community. Not officially affiliated with the Lean FRO. Lean is a trademark of Lean FRO, LLC.