Tutorial Contents Tutorial Three: Propositional Calculus: Tableaux - The Sentence Tableaux Rules - Testing Arguments for Validity - Sequents - Syntactic Sequents - Semantic Sequents - Soundness and Completeness - Correctness of Sequents and Validity of Arguments More Tutorials One Two Four Five Six Seven

Semantic sequents

A semantic sequent takes one of the following forms:

 (i) j1, j2, … |= y

(One can read this as saying that the set {j1, j2, …} semantically entails  y.)

 (ii) |= y

(One can read this as saying that y is a semantic theorem, or a tautology.)

 (iii) j1, j2, … |=

(One can read this as saying that the set {j1, j2, …} is semantically inconsistent.)

 The "|=" is the semantic turnstile.

A semantic sequent says, in effect, that there is no way of making all the formulae (if any) before the turnstile true and the formula (if any) after the turnstile false simultaneously. Let us be a little more precise. A structure in the propositional calculus is an assignment of truth-values to sentence letters. What a semantic sequent says is that there is no structure (which assigns truth-values to all the sentence letters in the sequent) which makes all the formulae (if any) before the turnstile true, and the formula (if any) after it false.

An easy (if sometimes laborious) way of checking for the correctness of semantic sequents is by using truth-tables. For instance we can check the correctness of

"[P«[QÙR]], [P®[¬Q®S]] |= [[QÙR]®S]" thus:

 P Q R S [P«[QÙR]] [P®[¬Q®S]] [[QÙR]®S] T T T T T     T T   F   T T     T T T F T T     T T   F   T T      F T T F T F     F T   F   T F     T T T F F F     F T   F   T F     T T F T T F     F T   T   T F     T T F T F F     F F   T   F F     T T F F T F     F T   T   T F     T T F F F F     F F   T   F F     T F T T T F     T T   F   T T     T F T T F F     T T   F   T T     F F T F T T     F T   F   T F     T F T F F T     F T   F   T F     T F F T T T     F T   T   T F     T F F T F T     F T   T   F F     T F F F T T     F T   T   T F     T F F F F T     F T   T   F F     T

From this one can see that there is a structure in which "[P«[QÙR]]" and  "[P®[¬Q®S]]" are both true and "[[QÙR]®S]" is false. (Look at the second row of the truth-table.) So the sequent  is incorrect.

We can, of course, speak of the counterexample set of a semantic sequent, just as we do in the case of syntactic sequents. The counterexample set consists, as you would expect, of all the formulae before the turnstile (if any) together with the negation of the formula after the turnstile (if there is one). We can also speak of a counterexample to a semantic sequent. A counterexample is a structure (which assigns truth-values to all the sentence letters in the sequent) which makes all the formulae (if any) before the turnstile true, and the formula (if any) after it false. In other words a counterexample to a sequent is a structure which makes all the formulae in the counterexample set true.
The text passage is a tutorial on propositional calculus, specifically discussing semantic sequents and how to check their correctness using truth tables. It includes an example of a truth table to demonstrate the process.
no_question

the passage does not contain a mathematical question or a request for a calculation. it provides an explanation and an example but does not ask the reader to solve a problem or perform a calculation.
Given a text passage, determine:
    1. If it contains a mathematical question (including word problems or calculations)
    2. If an answer to that mathematical question is provided in the text

First, describe the content structure you found in 1-2 sentences.

Then provide your analysis in the following format:
TYPE: <one of the following values>
- NO_QUESTION
- SINGLE_QUESTION
- SINGLE_QUESTION_WITH_ANSWER
- MULTIPLE_QUESTIONS
- MULTIPLE_QUESTIONS_WITH_ANSWERS
system
Tutorial Contents Tutorial Three: Propositional Calculus: Tableaux - The Sentence Tableaux Rules - Testing Arguments for Validity - Sequents - Syntactic Sequents - Semantic Sequents - Soundness and Completeness - Correctness of Sequents and Validity of Arguments More Tutorials One Two Four Five Six Seven

Semantic sequents

A semantic sequent takes one of the following forms:

 (i) j1, j2, … |= y

(One can read this as saying that the set {j1, j2, …} semantically entails  y.)

 (ii) |= y

(One can read this as saying that y is a semantic theorem, or a tautology.)

 (iii) j1, j2, … |=

(One can read this as saying that the set {j1, j2, …} is semantically inconsistent.)

 The "|=" is the semantic turnstile.

A semantic sequent says, in effect, that there is no way of making all the formulae (if any) before the turnstile true and the formula (if any) after the turnstile false simultaneously. Let us be a little more precise. A structure in the propositional calculus is an assignment of truth-values to sentence letters. What a semantic sequent says is that there is no structure (which assigns truth-values to all the sentence letters in the sequent) which makes all the formulae (if any) before the turnstile true, and the formula (if any) after it false.

An easy (if sometimes laborious) way of checking for the correctness of semantic sequents is by using truth-tables. For instance we can check the correctness of

"[P«[QÙR]], [P®[¬Q®S]] |= [[QÙR]®S]" thus:

 P Q R S [P«[QÙR]] [P®[¬Q®S]] [[QÙR]®S] T T T T T     T T   F   T T     T T T F T T     T T   F   T T      F T T F T F     F T   F   T F     T T T F F F     F T   F   T F     T T F T T F     F T   T   T F     T T F T F F     F F   T   F F     T T F F T F     F T   T   T F     T T F F F F     F F   T   F F     T F T T T F     T T   F   T T     T F T T F F     T T   F   T T     F F T F T T     F T   F   T F     T F T F F T     F T   F   T F     T F F T T T     F T   T   T F     T F F T F T     F T   T   F F     T F F F T T     F T   T   T F     T F F F F T     F T   T   F F     T

From this one can see that there is a structure in which "[P«[QÙR]]" and  "[P®[¬Q®S]]" are both true and "[[QÙR]®S]" is false. (Look at the second row of the truth-table.) So the sequent  is incorrect.

We can, of course, speak of the counterexample set of a semantic sequent, just as we do in the case of syntactic sequents. The counterexample set consists, as you would expect, of all the formulae before the turnstile (if any) together with the negation of the formula after the turnstile (if there is one). We can also speak of a counterexample to a semantic sequent. A counterexample is a structure (which assigns truth-values to all the sentence letters in the sequent) which makes all the formulae (if any) before the turnstile true, and the formula (if any) after it false. In other words a counterexample to a sequent is a structure which makes all the formulae in the counterexample set true.
user
The text passage is a tutorial on propositional calculus, specifically discussing semantic sequents and how to check their correctness using truth tables. It includes an example of a truth table to demonstrate the process.

TYPE: NO_QUESTION

The passage does not contain a mathematical question or a request for a calculation. It provides an explanation and an example but does not ask the reader to solve a problem or perform a calculation.