INTRODUCTORY-CHALLENGE-PROBLEM-1.html -- ACL2 Version 6.3

### INTRODUCTORY-CHALLENGE-PROBLEM-1

challenge problem 1 for the new user of ACL2

    Major Section:  INTRODUCTION-TO-THE-THEOREM-PROVER

Start in a fresh ACL2, either by restarting your ACL2 image from scratch or executing

    :ubt! 1

which will undo everything since the first user event.

Then define this function:

    (defun rev (x)
      (if (endp x)
          nil
          (append (rev (cdr x)) (list (car x)))))

Then use The Method to prove:

    (defthm triple-rev
      (equal (rev (rev (rev x))) (rev x)))

When you've solved this problem, compare your answer to ours; see introductory-challenge-problem-1-answer.

Then, use your browser's Back Button to return to introductory-challenges.