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Help on assignment 1

Posted by KeithF 
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Help on assignment 1
March 21, 2008 03:59PM
Right! Assignment 1 is just about done and dusted, with the exception of questions 12 and 15. Any hints?

Question 12 looks like it's asking us to prove De Morgan's theorem. Am I correct in this? Even then, I have no idea about how to tackle it.

Question 15: Drawing the DAG for a formula is not a problem, but how the heck do you draw a DAG for a sequent? Do you need to get it into a single formula? How do you do that?

Any tips would be most appreciated.
Re: Help on assignment 1
March 25, 2008 06:41PM
Yes I think 12 is de Morgan. I can't really help you with it unless I give you my solution - which might be wrong since I'm not very good at these.

What I did with 15 was link it all together as "If This and That then TheOther"
Re: Help on assignment 1
March 26, 2008 08:37AM
Thanks Jo,

I've got the first bit of De Morgens sorted, but the proving it in the other direction has me stumped (if that didn't make sense, then don't worry).

Just to clarify, the sequent is p V q, p -> r |- r

So, according to what you say, I should draw a DAG for

[(p V q) ^ (p -> r)] -> r

Looks about right, I guess...

Thanks for the help thumbs up
Re: Help on assignment 1
March 26, 2008 01:15PM
Sure Keith - that's what I did.

For De Morgan, going both ways, I started by assuming the negation of what I was trying to prove and ¬Q. Does that help?
Re: Help on assignment 1
March 26, 2008 01:33PM
Yup, that's what I'm doing (staring with ¬Q), but it only seems to work one way. I sure it's just a case of me having to sit with it a bit longer and trying a few different things.

Thanks again
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