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## #1 2011-07-06 08:21:31

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

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

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## #2 2011-07-06 09:49:12

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

hi iwan_ccie

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
The knowledge of some things as a function of age is a delta function.

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## #3 2011-07-06 09:57:16

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,037

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
The knowledge of some things as a function of age is a delta function.

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## #4 2011-07-06 10:07:06

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