Updated syntax.
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# Logic
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# Logic
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*Definition*: a statement is a sentence that is either true or false, never both.
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> *Definition*: a statement is a sentence that is either true or false, never both.
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<br>
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<br>
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*Definition* **- Implies**: if $A$ and $B$ are assertions then the assertion if $A$ then $B$ ($A \implies B$) is true iff
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> *Definition* **- Implies**: if $A$ and $B$ are assertions then the assertion if $A$ then $B$ ($A \implies B$) is true iff
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>
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* $A$ is true and $B$ is true,
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> * $A$ is true and $B$ is true,
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* $A$ is false and $B$ is true,
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> * $A$ is false and $B$ is true,
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* $A$ is false and $B$ is false.
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> * $A$ is false and $B$ is false.
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>
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This also works the opposite way, if $B$ then $A$ ($A \Longleftarrow B$)
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> This also works the opposite way, if $B$ then $A$ ($A \Longleftarrow B$)
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<br>
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<br>
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*Definition* **- If and only if**: if $A$ and $B$ are assertions then the assertion $A$ if and only if $B$ (A \iff B) is true iff
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> *Definition* **- If and only if**: if $A$ and $B$ are assertions then the assertion $A$ if and only if $B$ (A \iff B) is true iff
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>
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> * $(A \Longleftarrow B) \land (a \implies B)$.
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>
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> This leads to the following table.
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* $(A \Longleftarrow B) \land (a \implies B)$.
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| $A$ | $B$ | $A \implies B$ | $A \Longleftarrow B$ | $A \iff B$|
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| :---: | :---: | :------------: | :------------------: | :-------: |
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: This leads to the following table.
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| true | true | true | true | true |
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| true | false | false | true | false |
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| $A$ | $B$ | $A \implies B$ | $A \Longleftarrow B$ | $A \iff B$|
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| false | true | true | false | false |
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| :---: | :---: | :------------: | :------------------: | :-------: |
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| false | false | true | true | true |
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| true | true | true | true | true |
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| true | false | false | true | false |
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| false | true | true | false | false |
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| false | false | true | true | true |
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<br>
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<br>
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*Definition*: suppose $P$ and $Q$ are assertions. $P$ implies $Q$ if $P \implies Q$ is true. $P$ and $Q$ are equivalent if $P$ implies $Q$ and $Q$ implies $P$.
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> *Definition*: suppose $P$ and $Q$ are assertions. $P$ implies $Q$ if $P \implies Q$ is true. $P$ and $Q$ are equivalent if $P$ implies $Q$ and $Q$ implies $P$.
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## Methods of proof
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## Methods of proof
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