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Topic: universal quantification vs existential quantifier
Replies: 2   Last Post: Jul 28, 2013 5:12 PM

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Ken.Pledger@vuw.ac.nz

Posts: 1,383
Registered: 12/3/04
Re: universal quantification vs existential quantifier
Posted: Jul 28, 2013 5:12 PM
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In article <8951f688-4b18-4aaf-baa7-465af09f8ad0@googlegroups.com>,
shaoyi he <wubuqilai@gmail.com> wrote:

> ....
> if set S(X) is 'x is the class's student', C(x) is 'x has learned math'.
>
> so we cannot use (there exists x)(S(x)->C(x)) (domain: x is all people) shows some
> students of class have learned math. because S(x) is false (x is not the
> class's student), S(x)->C(x) is true....



The way to write "some student in the class has learned math"
is (there exists x)(S(x) and C(x)). Don't use implication for this one.

Ken Pledger.



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