Introduction to Proofs, an Inquiry-Based approach

A Free text for a course on proofs

Jim Hefferon
Mathematics Department, Saint Michael's College
jhefferon at

Introduction to Proofs is a Free undergraduate text. It is Inquiry-Based, sometimes called the Discovery Method or the Moore Method.


Here is Introduction to Proofs

Click to download the full Introduction to Proofs. You can instead get a compact version that prints onto seven sheets of paper. When I teach this class, I just hand this out on the first day.

There are beamer slides covering enough logic to get students started. You can also clone the repository, if you are into LaTeX.

What is "inquiry-based"?

This teaching style has students work directly with the mathematics.

I'll illustrate by discussing my version of this class. The students have four grades: one each from a mid-term and a final, a grade from the written work on their hand-in problems, and one reflecting their contributions to the in-class discussion. Thus the in-class work is the major part of the course — doing the exercises is the core experience.

Here is a typical day. As background, students have pledged not to work together or to use any resources such as other books, the net, students who have taken the course before, etc. Consequently, each day they arrive having worked on each exercise, on their own. Typical is four exercises. I shuffle index cards for who will go to the board.

While those students are writing their answers there are hand-in problems to collect, or in the first few classes beamer slides with some elementary logic, or perhaps questions about LaTeX (I distribute a LaTeX for Undergraduates). Or, sometimes we just talk about things, such as the Clay prizes, or news in the math world, or interesting blogs, or what math courses are offered next semester.

With the proposed answers up, the work begins. Students talk through the answers sentence by sentence and sometimes word by word. This discussion is filled with misconceptions that they need to worked out, bad ideas that take a while to go nowhere, and good ideas that perhaps have initial trouble getting a hearing. I speak as little as I can stand, I try not to nod or shake my head. (Sometimes I do guide, as with speaking up after the class has decided that the proof is OK to say, "In the second paragraph, exhibiting the n=3 and n=5 cases is not enough to show that in all cases the square of an odd is odd.")

But the discussion eventually comes to an end, the right end. The bonus is that students now understand why wrong things are wrong as well as having seen what is right.

The presented problems can take the entire period. If not then we do another. (Some exercises traditionally give people trouble, such as that there are infinitely many primes. I try to arrange things so we do these in class.)

Class ends with a new set of problems, perhaps once a week with the announcement that one of them to be handed in, and perhaps it must be done in LaTeX.

Let me close with three comments. First, I find that this style of teaching is harder than lecturing because I have surrendered the flow of control. But students learn better and that's the point, isn't it? The second comment is related: with this approach no matter where students fall on the bell curve, even at the end of the semester they are still engaged, still involved with the discussion and still understanding the point. In particular, I want that the students in this class who will go on to teach high school mathematics will have a solid understanding of proofs, including an understanding of when argument are wrong, and this approach gives me that assurance. Finally, I must acknowledge my debt to the Inquiry-based learning community and particularly to Prof Jensen-Vallin's wonderful Proofs book.

Can you help with Introduction to Proofs?

If you are an instructor who adopts this book then I'd be glad to hear your comments, including just the comment that you find it useful. (I save bug reports. and periodically revise.)

If you have some material that you are able to share back then I'd be interested to see it. Of course, I reserve the ability to choose whether to include it. I gratefully acknowledge all the contributions that I include, or I can keep you anonymous if you prefer. My email is jhefferon at


This text is Free. Use it under either the GNU Free Documentation License or the Creative Commons License Creative Commons Attribution-ShareAlike 2.5 License, at your discretion.

To bookstores: thank you for your concern about my rights. I give instructors permission to make copies of this material, either electronic or paper, and give or sell those copies to students. If you have further questions, don't hesitate to contact me at the email address on the top of this page.

To instructors: If you want to modify the text then feel free — that is one of my motivations for starting the project. However, I ask as a favor that you make clear which material is yours and which is mine. When I get questions or bug reports then having to work out what is happening gets frustrating all around unless the authorship is clear. It would be great if you could change the cover to include something like: " \fbox{The material in the appendix on logic is not from the main version of the text but has been added by Professor Jones of UBU. For this material contact \url{}.}"

You may also be interested in my Linear Algebra text, also Freely available. It is for a first US undergraduate course, covering the standard material while focusing on helping students develop mathematical maturity. It has been widely used for many years.

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This site Joshua is located in the Mathematics Department of Saint Michael's College in Colchester, Vermont USA.

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