[Mathematical logic] prenex normal form and skolem normal form

In summary, prenex normal form moves all quantifiers to the front of a logical formula, while skolem normal form eliminates existential quantifiers by introducing Skolem constants or functions. These forms are important in mathematical logic because they provide a simplified and standardized representation of logical formulas. To convert a formula into prenex normal form, one must eliminate implications and biconditionals, move negations inward, and use distributive laws to move disjunctions inward. To eliminate existential quantifiers for skolem normal form, one must rename bound variables and replace quantifiers with Skolem constants or functions. All logical formulas in first-order logic can be converted into these forms, but some may require numerous steps and result in complex formulas.
  • #1
Nico
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Homework Statement
[Mathematical logic] convert the following equation into prenex normal form and skolem normal form.
Relevant Equations
(a) ~∃x∃y(~p(x) ∧ ∀z q(y, z) )


(b) ∀x ( p(x) ⇔ ∃y q(y, x) )


(c) ~(∀p(x)∧∀y∃zq(y, z)∧∀y∃z q(z, y))
The attached picture below is the note I solved halfway through.

Please tell me the entire process of getting to the correct answer.
 

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  • #2
@Nico, we discourage the use of images that show work done, because they are usually illegible due to small image size or otherwise difficult to read.
Please show your work either as text or preferably, using LaTeX. There is a link to our tutorial at the lower left corner of the text entry pane.
 

FAQ: [Mathematical logic] prenex normal form and skolem normal form

What is prenex normal form in mathematical logic?

Prenex normal form is a standard form used in mathematical logic to represent logical formulas. It is named after the prenex quantifiers "forall" (∀) and "exists" (∃), which are used to quantify variables in the formula. In prenex normal form, all quantifiers are moved to the front of the formula, making it easier to analyze and manipulate.

How is prenex normal form different from skolem normal form?

While prenex normal form focuses on moving quantifiers to the front of a formula, skolem normal form goes a step further and eliminates existential quantifiers (∃) by introducing new skolem constants or skolem functions. This allows for a more efficient representation of logical formulas, particularly those involving existential quantifiers.

Why is it important to convert logical formulas into prenex normal form or skolem normal form?

Converting logical formulas into prenex normal form or skolem normal form can make them easier to analyze and manipulate. It also allows for more efficient logical reasoning and can help in identifying logical equivalences between different formulas. Additionally, many automated theorem proving systems and computer programs use prenex or skolem normal form as an intermediate step in their algorithms.

Can any logical formula be converted into prenex normal form or skolem normal form?

Yes, any logical formula can be converted into prenex normal form or skolem normal form. However, the resulting form may not always be unique. In some cases, there may be multiple equivalent forms that can be obtained through different conversion methods.

Are there any limitations or drawbacks to using prenex normal form or skolem normal form?

One limitation of prenex normal form is that it only works for first-order logic, which does not allow for nested quantifiers. Skolem normal form, on the other hand, can handle nested quantifiers but may introduce new constants or functions that may not have any intuitive meaning. Additionally, converting a formula into prenex or skolem normal form may result in a longer and more complex formula, making it harder to interpret and understand.

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