Brute force costs grow exponentially (well, combinatorically) with the number of terms. It's viable for the small cases, but not for the larger cases. There's a

Brute force costs grow exponentially (well, combinatorically) with the number of terms. It's viable for the small cases, but not for the larger cases. There's a nice paper from 2016 which demonstrates this very directly (http://www.cogsys.org/proceedings/2016/paper-2016-2.pdf http://www.cogsys.org/proceedings/2016/paper-2016-2.pdf), though I'm sure there's some stuff from the 70's on it as well.