PPT Slide
next_to( X , Y ) : - adjacent( X , Y ) .
next_to( X , Y ) : - adjacent( Y , X ) .
connected( A , B ) : - connect_mark( A , B , [ A ] ) .
connect_mark( A , B , Marked List ) : -
nonmember( B , Marked List ) ,
print( [ B ] Marked List ) .
connect_mark( A , B , Marked List ) : -
nonmember( C , Marked List ) ,
connect_mark( C , B , [ C ] Marked List ] ) .