The following cmavo is discussed in this section:
xi 
XI 
subscript 
The cmavo xi (of selma'o XI) indicates that a subscript (a number, a lerfu string, or a parenthesized mekso) follows. Subscripts can be attached to almost any construction and are placed following the construction (or its terminator word, which is generally required). They are useful either to extend the finite cmavo list to infinite length, or to make more refined distinctions than the standard cmavo list permits. The remainder of this section mentions some places where subscripts might naturally be used.
Lojban gismu have at most five places:
mi  cu  klama  le  zarci  le  zdani  le  dargu  le  karce  
I  go  to  the  market  from  the  house  via  the  road  using  the  car. 
Consequently, selma'o SE (which operates on a selbri to change the order of its places) and selma'o FA (which provides place number tags for individual sumti) have only enough members to handle up to five places. Conversion of Example 19.24, using xe to swap the x1 and x5 places, would produce:
le  karce  cu  xeklama  le  zarci  
The  car  isatransportationmeans  to  the  market 
le  zdani  le  dargu  mi  
from  the  house  via  the  road  for  me. 
And reordering of the place structures might produce:
fo  le  dargu  fi  le  zdani  fa  mi 
Via  the  road,  from  the  house,  I, 
fe  le  zarci  fu  le  karce  cu  klama 
to  the  market,  using  the  car,  go. 
Example 19.24 to Example 19.26 all mean the same thing. But consider the lujvo nunkla, formed by applying the abstraction operator nu to klama:
la'e  di'u  cu  nunkla  mi  
Thereferentof  theprevioussentence  isaneventofgoing  by  me 
le  zarci  le  zdani  le  dargu  le  karce  
to  the  market  from  the  house  via  the  road  using  the  car. 
Example 19.27 shows that nunkla has six places: the five places of klama plus a new one (placed first) for the event itself. Performing transformations similar to that of Example 19.25 requires an additional conversion cmavo that exchanges the x1 and x6 places. The solution is to use any cmavo of SE with a subscript "6" (Section 19.6):
le  karce  cu  sexixa nunkla  mi  
The  car  isatransportationmeansintheeventofgoing  by  me 
le  zarci  le  zdani  
to  the  market  from  the  house 
le  dargu  la'edi'u  
via  the  road  isaneventwhichisreferredtobythelastsentence. 
Likewise, a sixth place tag can be created by using any cmavo of FA with a subscript:
fu  le  dargu  fo  le  zdani  fe  mi 
Via  the  road,  from  the  house,  by  me, 
fa  la'edi'u  
isaneventwhich  isreferredtobythelastsentence, 
fi  le  zarci  faxixa  le  karce  cu  nunkla 
to  the  market,  using  the  car,  isaneventofgoing. 
Example 19.27 to Example 19.29 also all mean the same thing, and each is derived straightforwardly from any of the others, despite the tortured nature of the English glosses. In addition, any other member of SE or FA could be substituted into sexixa and faxixa without change of meaning: vexixa means the same thing as sexixa.
Lojban provides two groups of prosumti, both belonging to selma'o KOhA. The ko'aseries cmavo are used to refer to explicitly specified sumti to which they have been bound using goi. The daseries, on the other hand, are existentially or universally quantified variables. (These concepts are explained more fully in Chapter 16.) There are ten ko'aseries cmavo and 3 daseries cmavo available.
If more are required, any cmavo of the ko'aseries or the daseries can be subscripted:
is the 4th bound variable of the 1st sequence of the daseries, and
is the 18th free variable of the 3rd sequence of the ko'aseries. This convention allows 10 sequences of ko'atype prosumti and 3 sequences of datype prosumti, each with as many members as needed. Note that daxivo and dexivo are considered to be distinct prosumti, unlike the situation with sexixa and vexixa above. Exactly similar treatment can be given to the bu'aseries of selma'o GOhA and to the gismu probridi broda, brode, brodi, brodo, and brodu.
Subscripts on lerfu words are used in the standard mathematical way to extend the number of variables:
li  xy.boixipa  du  li  xy.boixire  su'i  xy.boixici  
Thenumber  xsub1  equals  thenumber  xsub2  plus  xsub3  
x_{1} = x_{2} + x_{3}

and can be used to extend the number of prosumti as well, since lerfu strings outside mathematical contexts are grammatically and semantically equivalent to prosumti of the ko'aseries. (In Example 19.32, note the required terminator boi after each xy. cmavo; this terminator allows the subscript to be attached without ambiguity.)
Names, which are similar to prosumti, can also be subscripted to distinguish two individuals with the same name:
la  djan.  xipa  cusku  lu  mi'enai  do  li'u  la  djan.  xire  
John  _{1}  expresses  [quote]  Iamnot  you  [unquote]  to  John  _{2}  . 
Subscripts on tenses allow talking about more than one time or place that is described by the same general cmavo. For example, puxipa could refer to one point in the past, and puxire a second point (earlier or later).
You can place a subscript on the word ja'a, the bridi affirmative of selma'o NA, to express socalled fuzzy truths. The usual machinery for fuzzy logic (statements whose truth value is not merely “true” or “false”, but is expressed by a number in the range 0 to 1) in Lojban is the abstractor jei:
However, by convention we can attach a subscript to ja'a to indicate fuzzy truth (or to na if we change the amount):
Finally, as mentioned in Section 19.2, ni'o and no'i cmavo with matching subscripts mark the start and the continuation of a given topic respectively. Different topics can be assigned to different subscripts.
Other uses of subscripts will doubtless be devised in future.