Example
Show that
and
are logically equivalent.
( ( )
( ))
x P x
Q x
( ( )
( ))
( ( )
( ))
(De Morgan)
x P x
Q x
x
P x
Q x
(
( )
( ))
(convert)
x
P x
Q x
( ( )
( ))
x P x
Q x
( (
( ))
(
( )))
(De Morgan)
x
P x
Q x
( ( )
( ))
(double negation)
x P x
Q x

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Rules of Inference: Terms
An
argument
is a sequence of statements that end with
a conclusion.
An argument is
valid
if the conclusion follows from the
truth of the preceding statements.
That is, an argument is valid if and only if it is impossible
for the preceding statements (premises) to be true while
the conclusion is false.
A
fallacy
is a common form of incorrect reasoning,
which lead to invalid arguments.

Rules of Inference I

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Rules of Inference II