# Thread: Quick logic question

1. ## Quick logic question

How can i write A /\ B (A and B) using only the signs for negation and the sign for if then (the right facing arrow)

I know i am supposed to use the changing laws but i cant figure out how.

Regards

2. Originally Posted by Monika1987
How can i write A /\ B (A and B) using only the signs for negation and the sign for if then (the right facing arrow)

I know i am supposed to use the changing laws but i cant figure out how.

Regards
$\displaystyle \neg( A \Rightarrow B ) \Longleftrightarrow A \wedge \neg B$ --- you can check this with table of truth ( i think that is the term in english, maybe not ( it is just literal translation from my language ) )

so

you need $\displaystyle A \wedge B \Longleftrightarrow A \wedge \neg(\neg B) \Longleftrightarrow \neg( A \Rightarrow \neg B )$

what a mistake!!!

3. Originally Posted by Monika1987
How can i write A /\ B (A and B) using only the signs for negation and the sign for if then (the right facing arrow)
Actually it is $\displaystyle A \wedge B \equiv \neg \left( {A \to \neg B} \right)$.