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**dangermulan1988****Member**- Registered: 2011-06-11
- Posts: 18

please delete

*Last edited by iwan_ccie (2011-07-11 01:38:34)*

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,657

hi iwan_ccie

first one is a contradiction

second one is a contradiction

third one is a tautology

fourth one is contingent

and the fifth one is also contingent.

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

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**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,657

hi iwan_ccie

there are several ways to determine if a proposition is a tautology or a contradiction.

the easiest one is to make a table,make columns for all the boolean variables and then plug them into the equation and if the equation is always true then it is a tautology,and if it is always incorrect than it is a contradiction.

the other one works only when you have to prove that it is a tautology.it is called *reductio ad absurdum*.

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

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**dangermulan1988****Member**- Registered: 2011-06-11
- Posts: 18

Thanks for your answer!

So you created truth tables?

Can you show me how you did this? And how you determined the answers?

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