If you already knew everything I explained, or have doubts about other topics unrelated to the way of doing natural deduction, stay at this section.

- 8.1 Why is it called natural deduction?
- 8.2 Is the solution unique?
- 8.3 Other ways to prove validity

- 8.4 How to prove invalidity
- 8.5 Create your own exercises
- 8.6 Programs which do natural deduction

Daniel Clemente Laboreo 2005-05-17