|s1> => find-topic[words-2] (|thomas jefferson>)
|s2> => find-topic[words-2] (|thomas jefferson> + |ronald regan>)
|s3> => find-topic[words-2] (|thomas jefferson> + |ronald regan> + |richard nixon>)
|s4> => find-topic[words-2] (|thomas jefferson> + |ronald regan> + |richard nixon> + |bill clinton>)
|s5> => find-topic[words-2] (|thomas jefferson> + |ronald regan> + |richard nixon> + |bill clinton> + |barack obama>)
|s6> => find-topic[words-2] (|thomas jefferson> + |ronald regan> + |richard nixon> + |bill clinton> + |barack obama> + |george washington>)
|s7> => find-topic[words-2] (|thomas jefferson> + |ronald regan> + |richard nixon> + |bill clinton> + |barack obama> + |george washington> + |james monroe>)
|s8> => find-topic[words-2] (|thomas jefferson> + |ronald regan> + |richard nixon> + |bill clinton> + |barack obama> + |george washington> + |james monroe> + |jimmy carter>)
|list> => |s1> + |s2> + |s3> + |s4> + |s5> + |s6> + |s7> + |s8>