Wiki-ch2

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Additional Wiki pages for Chapter 2

Models

The following material is an adapted form of material created by student participants of the project e-Learning Resources for Semantics (e-LRS). Involved participants: Lisa, Marthe, Elisabeth, Isabelle.

Watch a short podcast what first-order models look like.

<mediaplayer>http://youtu.be/4a3mXelw7H4</mediaplayer>

Truth tables

The following material is an adapted form of material created by student participants of the project e-Learning Resources for Semantics (e-LRS). Involved participants: Lisa, Marthe, Elisabeth, Isabelle.

Truth tables for connectives

AND (∧)

Symbol: ∧
Sentence: Harry is a student and Snape is a teacher.
Formulae: student(harry) ∧ teacher(snape)

A conjunction pq it true if and only if p is true and q is true.

Truthtable AND

Truthtable AND1.png

OR (∨)

Symbol: ∨
Sentence: Harry is a student or Snape is a teacher.
Formulae: student(harry) ∨ teacher(snape)

A disjunction pq is true if and only if p is true or q is true (or both).

Truthtable OR

Truthtable OR1.png

IF/THEN (⊃, →)

Symbol: ⊃, → (Note: We use the symbol ⊃ in the textbook as it is more common in the logical literature.)
Sentence: If Harry is a student then Snape is a teacher.
Formula: student(harry) ⊃ teacher(snape)

An implication pq is true if and only if p is false or q is true (or both).
In other words: An implication pq is true if and only if whenever p is true, q is true as well.

Truthtable IF/THEN

Truthtable IF THEN2.png

NOT (¬)

Symbol: ¬
Sentence: Harry is not a student.
Formula: ¬student(harry)

A negated formula ¬p is true if and only if p is false.

Example: Only if student(harry) is false, ¬student(harry) is true.


Truthtable NOT

Truthtable NOT.png

Truth tables for complex formulae

Truth tables are also useful to compute the truth value of complex formulae. This is shown in the following podcast, created by Lisa Günthner.

<mediaplayer>http://www.youtube.com/watch?v=ZWdltj5Mqdc</mediaplayer>