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I am learning CNF and I have a teacher who is doing something I truly don't understand. I want to ask him later on, yet I am struggling to finish my coursework so it can't wait until then.

So..

 -A --> B

It needs to be -A v B. This one... this one is fine, I get it.

The thing starts when he goes further and says that it needs to be: -A, B... and, after that, A,B

And I am stunned. How does he get -A, B and derive A,B from that? And on Wikipedia, I can't read anything about changing -A v B to something else...

Can someone help me by confirming that I am right and that it should be -A v B... and only that?

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    'Negation A, B' is not a logic statement ... nor is 'A, B' ... I don't know what your teacher is trying to do here, but it doesn't look like an inference, if you think that's what it is. – 2017-01-22
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    He calls it "verder kleiner maken", but I don't get why on earth that is needed. So he makes them smaller, but I am stunned to be honest. Am I correct when I say that -A v B is the ONLY good answer here? – 2017-01-22
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    Do you have some notes you could copy or take a picture of? – 2017-01-22
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    Nope, I am afraid I have not. I'll ask them and won't confuse anyone else here haha. Thanks for the reactions. – 2017-01-22
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    @Siyah Also check this to visualize your code: http://pythontutor.com/visualize.html#mode=display – 2017-02-05
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    @MYGz: thanks mate, I've sent you an e-mail. – 2017-02-05

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I think I see what is going on ...

OK, we have that:

$A \rightarrow B \Leftrightarrow \neg A \lor B$ (you can use a truth-table to verify this)

But that means:

$\neg A \rightarrow B \Leftrightarrow$

$\neg \neg A \lor B \Leftrightarrow$

$A \lor B$

Is that maybe what your instructor is trying to do?

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    Perhaps, yes, but how do yet get double negation A when you only have negation A --> B? I mean, where are these rules? Where can I find a good site where ALL the rules are explained? – 2017-01-22
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    @Siyah I was thinking that maybe he started out with $\neg A \rightarrow B$ instead of $A \rightarrow B$ so you would get an extra negation when converting to an $\lor$, and hence a double negation – 2017-01-22
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    Ah, got it. No, he didn't start like that, I am sure of that, but I'll just ask him. He confused me. – 2017-01-22
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    @Siyah There are lots of sites ... look for 'Boolean Algebra rules' or 'logical equivalence rules'. – 2017-01-22
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    @Siyah You're welcome ... or should I say 'Graag gedaan!'? – 2017-01-22
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    Haha, I knew you were Dutch already. Thanks Bram, ik waardeer het. – 2017-01-22
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    @Siyah :). And just to make sure: I am sure that there is nothing 'weird' going on; you can't just drop negations unless it is a double negation of course. So, either your instructor forgot to write down a negation or you forgot to copy some negation. Anyway, don't worry that there is something you are not understanding! – 2017-01-22
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    That's what I though too. It will be more clear this week, merci! – 2017-01-22
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    @Siyah OK; let me know what you find out, just for my own interest! – 2017-01-22
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    you were right, he just started like that indeed. – 2017-02-12
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    @Siyah Good! So nothing strange happened :) Thanks for getting back to me. – 2017-02-12
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    I did, thanks Bram. – 2017-02-12