In the following exercises: $($a$)$ use the logical equivalences $pqpvvq$ and pharrq$-=(pvvq{)}^{{?}^{?}}(qvvp)$ to rewrite the given statement forms without using the symbol $$ or harr, and $($b$)$ use the logical equivalence $pvvq(p^{{?}^{?}}q)$ to rewrite each statement form using only ${?}^{{?}^{?}}$ and $.$

$($a$)p^{{?}^{?}}qr$

$($b$)pvvqrvvq$

$($c$)(pr)harr(qr)$

$($d$)(p(qr))harr((p^{{?}^{?}}q)r)$