1.2 Why do I write this

Some reasons:

• There's a big gap in the search ``natural deduction'' at Google. I myself needed to study it before the exam, but couldn't find anything useful which helped me. There actually existed some tutorials, but no one was good enough (in my opinion): some were too confusing, others had special characters which didn't display correctly, and others didn't explain everything (as if everyone knew all the logic concepts). So I decided to create this tutorial which I hope it will help someone.
• It's a topic I like, and can do without much problems.
• It makes you think. Maybe it hasn't got a lot of practical uses, but one really has to try hard and spend some time in order to solve some simple problems.
• Well, I confess that I wrote this to learn text processing with L^ATEX. You need some dedication to learn it, but the results make the work be worth it.