LI (http://www.lojban.org/en/publications/reference_grammar/chapter18.html)

Descriptors which change numbers or other mathematical expressions into sumti
which specify numbers or numerical expressions. See LOhO.

li re su'u re na du li vo su'i vo the-number 2 minus 2 not equals the-number 4
plus 4. $2 - 2 <> 4 + 4$

