Discrete Math 1 - Tutorial 38 - Quantifiers Example

Quantifiers, Existential Quantifier, Universal Quantifier Example

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[greenm]

1/2 is a rational number not a positive integer, Not sure what you mean 
by positive real integers, do you mean real numbers included? which would make
saying integers pointless.. Since you can say positive real numbers, which would allow the use of the rational number in that universe.

[etime]

1/2 is not an integer - is it? I thought 1/2 was a rational number and that positive real integers are basically whole numbers. So 1/2 is not in the universe of positive real integers, therefore it cannot be used as a counterexample. Am I right?

[virginia]

Thanks. V helpful except for the dual; wasn't clear why the dual is useful 

[zhaoningding]

please correct the mistake! 1/2 is not a positive integer man!