$3.$ Consider the following definite Horn$-$clause KB:

$$x$$y$$z Parent$($x$,$y$)$ & Parent$($x$,$z$)$ & y$!=$z $=>$ Sibling$($y$,$z$)$

$$x$$y$$z Sibling$($v$,$w$)$ & Parent$($w$,$u$)$ & Male$($u$)=>$ Nephew$($u$,$v$)$

Parent$($Bob$,$Mary$),$ Male$($Bob$),$ Female$($Mary$),$ Parent$($Bob$,$Fred$),$ Male$($Fred$),$ Parent$($Mary$,$Tom$),$ Male$($Tom$),$ Parent$($Mary$,$Ann$),$ Female$($Ann$)$

Assume backward$-$chaining rule$-$based inference is used to try to answer the query: Nephew$($s$,$Fred$).$