only thinking; then write it down on paper. It's something like:
I will put it by words: ``if you use Linux and Mozilla as
a browser, you avoid problems. In contrast, if you use Internet Explorer
you will have problems. Now you use Mozilla, but also Internet Explorer
sometimes. Consequently, I know that you don't use Linux''.
Maybe that seems evident: ``of course, since IE is not on
Linux'', but notice that I never said that. There isn't the
The way in which you should think when you prepare this exercise is:
Now you just have to follow the same procedure, but writing down each
step, and using the derivation rules. What you will obtain is the
figure above, which happens to have 5 procedure lines (the first 4
are only to copy the truths). Each line corresponds with the steps
- I need to prove, which is the negation of something. It can't
be seen any rule of the form something implies which
allows me to obtain it directly. We should think of another way, for
example negation introduction (reduction to the absurd):
suppose that I do use Linux.
- In the case when I use Linux, I would use both Linux and Mozilla,
since I already used Mozilla before (it's the third truth which is
written in the original problem).
- Using both Linux and Mozilla, I wouldn't have computer problems, since
- But I also used Internet Explorer (fourth truth), and since IE generates
problems, I will have problems. .
- I got a contradiction: and . So, what's happening is
that the supposition I did of using Linux is wrong: actually, .
Daniel Clemente Laboreo