Rewrite these propositions wih equivalence:
$a:(b \, \lor \, c) \Rightarrow (\lnot b \, \lor \, \lnot c)$
$b: (\lnot c \, \lor \, q) \Rightarrow r$
$c: a \Rightarrow (\lnot q \, \land \lnot r)$
I got statements which I have to write in the form of equivalence. I translate the statements into the formulas above, but I don't know how can I make equivalence from these formulas.
I tried to substitute $a$ and $b$ to proposition $c$ but it didn't lead to anywhere.
We have implication above and we know that equivalence is: both $p \Rightarrow q$ and $q \Rightarrow p$ but I am not really sure how can I change it into equivalence.