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何少仪
Posts:
6
Registered:
7/21/13


universal quantification vs existential quantifier
Posted:
Jul 28, 2013 12:16 AM


i delete former post, beacuse it's format.
if set S(X) is 'x is the class's student', C(x) is 'x has learned math'.
so we cannot use ?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.
but why can i use ?x(S(x)>C(x)) (domain: x is all people) shows all the class's student have learned math, beacuse S(x) is false (x is not the class's student), S(x)>C(x) is also true?



