Lojban has a separate grammar embedded within the main grammar for representing mathematical expressions (or mekso in Lojban) such as “2 + 2”. Mathematical expressions are explained fully in Chapter 18. The basic components of mekso are operands, like “2”, and operators, like “+”. Both of these may be either logically or nonlogically connected.
Operands are connected in afterthought with eks and in forethought with geks, just like sumti. Operators, on the other hand, are connected in afterthought with jeks and in forethought with guheks, just like tanru components. (However, jeks and joiks with bo are not allowed for operators.) This parallelism is no accident.
In addition, eks with bo and with ke…ke'e are allowed for grouping logically connected operands, and ke…ke'e is allowed for grouping logically connected operators, although there is no analogue of tanru among the operators.
Only a few examples of each kind of mekso connection will be given. Despite the large number of rules required to support this feature, it is of relatively minor importance in either the mekso or the logicalconnective scheme of things. These examples are drawn from Section 18.17, and contain many mekso features not explained in this chapter.
Example 14.149 exhibits afterthought logical connection between operands:
Example 14.150 is equivalent in meaning, but uses forethought connection:
Note that the mekso in Example 14.149 and Example 14.150 are being used as quantifiers. Lojban requires that any mekso other than a simple number be enclosed in vei and ve'o parentheses when used as a quantifier. The right parenthesis mark, ve'o, is an elidable terminator.
Simple examples of logical connection between operators are hard to come by. A contrived example is:
li  re  su'i  je  pi'i  re  du  li  vo 
Thenumber  2  plus  and  times  2  equals  thenumber  4. 
2 + 2 = 4 and 2 x 2 = 4. 
The forethought form of Example 14.151 is:
li  re  ge  su'i  gi  pi'i  re  du  li  vo 
Thenumber  two  both  plus  and  times  two  equals  thenumber  four. 
Both 2 + 2 = 4 and 2 x 2 = 4. 
Nonlogical connection with joiks or joigiks is also permitted between operands and between operators. One use for this construct is to connect operands with bi'i to create mathematical intervals:
li  no  ga'o  bi'i  ke'i  pa  
thenumber  zero  (inclusive)  fromto  (exclusive)  one  
[0,1)

the numbers from zero to one, including zero but not including one 
You can also combine two operands with ce'o, the sequence connective of selma'o JOI, to make a compound subscript:
Note that the boi in Example 14.154 is not elidable, because the xi subscript needs something to attach to.