The questions are:
1) Is it true?
2) Can you absolutely know that it is true?
3) How do you react, what happens, when you believe that thought?
4) Who would you be without the thought?

She then has you turn the concept you are questioning around.

Bryon Katie has written several books on the subject and we HIGHLY recommend them!

Here are three of the books:

Loving What Is: This book tells the story of how Katie discovered the work. It also teaches the process of how to do the work and gives examples of people doing the work with Katie.

Who Would You Be Without Your Story: A collection of 15 examples of people doing the work with Katie.

A Thousand Names For Joy: This is a radically different book than the first two we’ve described here. It doesn’t focus on the work as much as it explores the freedom that comes from doing the work. Katie’s husband, Stephen Mitchell published his own translation of the famous “Tao Te Ching” and as he was reading it to Katie, she took concepts from it and elaborated on her view of it. If you love the Tao Te Ching, you’ll really love this book!