Nested Quantifier Question

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  • Thread starter SamitC
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Main Question or Discussion Point

Hello,
Suppose a problem statement is :

In a school, suppose S(x) is “x is a student”, F(x) is “x is a faculty member” and A (x, y) is “x asked a question to y”. Domain is all the people associated with the school. Write the following using quantifiers:
"Some student did not ask any faculty member a question".

Answers are:

So, ∃x [S(x) ∧ ∀y {F(y) → ¬ A(x, y)}] OR ∃x [S(x) ∧ ¬∃y {F(y)A(x, y)}]

Instead, if we bring all the quantifiers at the front, will it cause any difference? Like:
xy [S(x) ∧ {F(y) → ¬ A(x, y)}] OR ∃x ¬∃y [S(x) ∧ {F(y)A(x, y)}]

In general, does it ever cause any change in looping if we bring all quantifiers at the front? Or is there any specific reason not to put all quantifiers at the front?

Thanks
 

Answers and Replies

  • #2
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In this case it doesn't make a difference, but sometimes it can make the expressions harder to read because you have to remember all the variables and their quantifiers before they are actually used.

There could be expressions where it makes a difference, although I don't have an example right now.
 
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In this case it doesn't make a difference, but sometimes it can make the expressions harder to read because you have to remember all the variables and their quantifiers before they are actually used.

There could be expressions where it makes a difference, although I don't have an example right now.
Thank you.
 

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