# Difference between revisions of "Logic"

Logic is the systematic use of symbolic and mathematical techniques to determine the forms of valid deductive or inductive argument.

## Statements

A statement is either true or false, but it will never be both or neither. An example of statement can be "A duck is a bird." which is true. Another example is "A pencil does not exist" which is false.

## Logical Notations

Main article: Logical notation

A Logical notation is a special syntax that is shorthand for logical statements.

## Negations

A negation is denoted by $\neg p$. $\neg p$ is the statement that is true when $p$ is false and the statement that is false when $p$ is true. This means simply "the opposite of $p$"

## Conjunction

The conjunction of two statements basically means " $p$ and $q$" and is denoted by $p \land q$.

## Disjunction

The disjunction of two statements basically means " $p$ or $q$"

## Implication

This operation is given by the statement "If $p$, then $q$". It is denoted by $p\Leftrightarrow q$

## Converse

The converse of the statement $p \Leftrightarrow q$ is $q \Leftrightarrow p$.

## Contrapositive

The contrapositive of the statement $p \Leftrightarrow q$ is $\neg p \Leftrightarrow \neg q$

## Quantifiers

There are two types of quantifiers: $\dot$ (Error compiling LaTeX. ! Extra }, or forgotten $.) Universal Quantifier: "for all"$\dot$(Error compiling LaTeX. ! Extra }, or forgotten$.) Existential Quantifier: "there exists"