John Woldemar Cowan, The Complete Lojban Language — Chapter 2 - The concept of the bridi (1997)
“ There is a problem when we want to say “The fast one is talking.” The “obvious” translation “le sutra tavla” turns out to mean “the fast talker”, and has no selbri at all. To solve this problem we can use the word “cu”, which so far has always been optional, in front of the selbri.The word “cu” has no meaning, and exists only to mark the beginning of the selbri within the bridi, separating it from a previous sumti. It comes before any other part of the selbri, including other cmavo like “se” or “te”. ”
