Consider a relation R $=\{$P$,$ Q$,$ R$,$ S$,$ T$,$ U$,$ V$,$ W$\}$ with

the functional dependency sets S $=\{$PR$->$V$,$ S$->$TV$,$

QR$->$S$,$ RV$->$QS$,$ PRS$->$Q$,$ RT$->$PV$\}$

The minimum numbers of simple functional

dependency in the minimal cover of F is $\_\_\_\_\_\_\_\_\_?$