stumbled across this on my exercise sheet:
was just wondering if anyone could show me how to do (a) so i can attempt the rest?
i've written the answer down as Ex (S(x) => K(x, logic)) but need someone to clarify for me whether i've done this correct. if not, where have i gone wrong?
thanks in advance for any help
predicate logic question
Page 1 of 14 Replies  1957 Views  Last Post: 07 May 2013  07:15 AM
Replies To: predicate logic question
#2
Re: predicate logic question
Posted 05 May 2013  05:14 AM
First of all you're missing a quantifier for x. As it stands now, your x comes out of nowhere.
There's another mistake, but it's easier to explain why it's wrong, once you've picked a quantifier, so do that first.
There's another mistake, but it's easier to explain why it's wrong, once you've picked a quantifier, so do that first.
#3
Re: predicate logic question
Posted 06 May 2013  10:43 PM
Quote
First of all you're missing a quantifier for x. As it stands now, your x comes out of nowhere.
I think he is using "E" as the existential quantifier. Perhaps you are referring to the fact that he does not specify "There exists an x in domain"? Though it may seem sloppy, it is actually valid notation to leave off the domain that x belongs to and just say "There exists x". In such cases, the domain must be implied. In this example, there is only one domain so it is automatically implied.
@Idonknow, the problem with your statement is that it is true if there is a student that knows logic, or if x is not a student. So, even if no students knew logic, your statement would still be true for mary and sue. You need to make a statement that is false if no students know logic.
#4
Re: predicate logic question
Posted 07 May 2013  06:53 AM
#5
Re: predicate logic question
Posted 07 May 2013  07:15 AM
Even so, in most cases, you deal with a domain and a codomain, and explicit is almost always better than implicit, so saying that there exists a value in the domain versus codomain is almost always relevant
∃ x ∈ Domain: S(x) => K(x, logic)
would be correct here.
∃ x ∈ Domain: S(x) => K(x, logic)
would be correct here.
This post has been edited by Dogstopper: 07 May 2013  07:17 AM
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