John Woldemar Cowan, The Complete Lojban Language (2016)
“ As a brivla, a lujvo must also contain a consonant cluster within the first five letters – this ensures that they cannot be mistaken for compound cmavo. Of course, all lujvo have at least six letters since they have two or more rafsi, each at least three letters long; hence they cannot be confused with gismu. When attaching two rafsi together, it may be necessary to insert a hyphen letter. In Lojban, the term “hyphen” always refers to a letter, either the vowel y or one of the consonants r and n. (The letter l can also be a hyphen, but is not used as one in lujvo.) ”
