To Fix a Mockingbird


After reading Smullyan's deep, delightful book To Mock a Mockingbird and going through all of the exercises therein, I realised I had spotted quite a list of typos, errors, notational inconsistencies, and so on.

A few times, stumbling upon such a glitch in the text, I even tried to find confirmation for my corrections out there in the Internet, only to discover, with my utter amazement and despair, that only in very few cases was there already, somewhere, written proof that someone had noticed the inconsistency and left notice of the correction for the future travellers of the same routes.

So I decided to collect here, in this documentation, all the corrections I would make, in pencil, on a newly-bought copy of the book were I to hand it, as a gift, to a friend. The aim would be not to spoil their enjoyment of the marvelous book but, rather, to make it smoother and less fragmentary.

As a disclaimer to this introduction, I hereby do not want, by any means, to diminish the value of the book, which I deem one of the best readings of my recent life; nor do I claim that this list of corrections is perfect: it may well be that some are plain wrong and that some are missing.

I can also absolutely not claim that it's all my own work: there are some corrections, listed here, for which I sought guidance in other people's commentaries on the internet. For these, due credit is specified in the fix list, whenever I was able to track the origin.

Of course I am open to comments and corrections and will try to incorporate them in the present document, trying to always give full credits where due, with the intent of making this document an up-to-date erratum list for the book.

Reference edition

Book Cover

For definiteness (although I suspect most of the errata applies to other editions as well), the edition I use as reference, including page numbers, is the following:

To mock a Mockingbird and other logic puzzles
Raymond Smullyan
Oxford University Press

Here are relevant excerpts from the fourth paper page (i.e. not counting the paperback cover):

    First published 1985 as a Borzoi Book by Alfred A. Knopf. Inc. New York
    First issued as an Oxford University Press Paperback 1990
    Reissued 2000
    ISBN 978-0-19-280142-5
    Printed in Great Britain by
    Clays Ltd, St Ives plc

and a couple useful details from the last page before the closing paperback cover (the first is the number reported in the barcode):

    printed in Great Britain by Amazon


I divided the entries of the fix list according to the following categories:

  • Typos: notational inconsistencies, trivial corrections most likely due to typesetting errors (but nonetheless, sometimes, able to get in your way while following a proof).
  • Formula/proof errors: those provide a wrong starting point, severely compromise the unfolding of the reasoning, or give a wrong final result.
  • Immediate additions: alternative solutions (as good as the provided one), non-vital remarks or limitations of the provided reasoning, further clarification steps.
  • Out-of-one's way bonuses: solution to additional exercises given as end-of-chapter training material, bonus material (e.g. computer programs) merely hinted at, and so on.
  • Open questions: issues sparked by the material encountered in the book for which I could not find a definite answer.


The material you are reading is also publicly available as a github repository.

For any communication, I advise you to reach me through my github account.