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Which of the following well-formed formulas are equivalent?

1. $P \rightarrow Q$
2. $\neg Q \rightarrow \neg P$
3. $\neg P \vee Q$
4. $\neg Q \rightarrow P$
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A,B and C are equivalent

1. $P→Q \equiv \neg P\vee Q$
2. $¬Q→¬P\equiv Q\vee \neg P$
3. $¬P\vee Q \equiv \neg P \vee Q$

So, $A,B,C$ are equivalent .

selected
A,B,C are equavelent i.e. $P\rightarrow Q \equiv \sim P \vee Q$

A and C are equal because if $\rightarrow$ is true then Contradiction always true.
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D is not equivalent
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How D?
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i was taken as  $\sim$(Q $\rightarrow$ P)
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That is also not true.
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I know that sir Or wil changes to And. thats why changed that.

A) P→Q <=> ~P $\vee$ Q

B) ¬Q→¬P <=>~(~Q) $\vee$~P <=> Q $\vee$ ~P <=> ~P $\vee$ Q         [ ~(~A)=A ]

C) ¬P $\vee$ Q

D) ¬Q → P <=>~(~Q) $\vee$ P <=> Q $\vee$ P

So, You see above