But then I look at
http://vlasisku.lojban.org/cimei and it says that x1 is a set. So if I talk about {lo cimei gerku cu batci lo mripre} am I saying that as a mass, the three dogs bit the mailman or am I saying that the set of three dogs bites the mailman?
I forget some of the differences between sets and masses. I think if a set of 3 things does a thing then all 3 must have done it individually where as long as 1 of a mass of 3 does a thing then the entire mass has done it. So there is certainly a difference in meaning.