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Why this the following not a tautology? There is no case in which RHS is False and LHS is True.

$\Bigl [ (\lnot p \land q) \land \bigl[ q \to (p \to q) \bigr ] \Bigr ] \to \lnot r$
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You can see that when $p=0, q=1, r=1$, the LHS is True but the RHS is False.

You can reduce the original equation as follows, which also should tell you how you can arrive at those values for the variables.

$$\begin{align}
&\Bigl [ (\lnot p \land q) \land \bigl[ q \to (p \to q) \bigr ] \Bigr ] \to \lnot r \\[1em]
\equiv& \Bigl [ \bar p \cdot q  \cdot \bigl[ q \to (p \to q) \bigr ] \Bigr ] \to \bar r & \text{easier notation}\\[0.5em]
\equiv& \Bigl [ \bar p \cdot q  \cdot \bigl[ \bar q + (p \to q) \bigr ] \Bigr ] \to \bar r & x \to y \equiv \bar x + y\\[0.5em]
\equiv& \Bigl [ \bar p \cdot q  \cdot \bigl[ \bar q + (\bar p + q) \bigr ] \Bigr ] \to \bar r \\[0.5em]
\equiv& \Bigl [ \bar p \cdot q  \cdot \bigl[ 1 \bigr ] \Bigr ] \to \bar r & \bar x + x \equiv 1\\[0.5em]
\equiv& \Bigl [ \bar p \cdot q\Bigr ] \to \bar r & x \cdot 1 \equiv x\\[0.5em]
\equiv& \overline {( \bar p \cdot q)} + \bar r \\[0.5em]
\equiv& ( p + \bar q) + \bar r & \overline{x\cdot y} \equiv (\bar x + \bar y), \quad \bar{\bar x} = x\\[0.5em]
\not \equiv& 1
\end{align}$$
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hitendra singh asked Oct 22, 2018
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State T/F:1- Every satisfiable is a contingency2- Every satisfiable is a Tautology.