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Re: universal quantification vs existential quantifier
Posted:
Jul 28, 2013 5:12 PM


In article <8951f6884b184aafbaa7465af09f8ad0@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.



