## Chapter 18: lojbau mekso: Mathematical Expressions in Lojban

### 13. Subscripts

The following cmavo is discussed in this section:

`xi  XI  subscript`

Subscripting is a general Lojban feature, not used only in mekso; there are many things that can logically be subscripted, and grammatically a subscript is a free modifier, usable almost anywhere. In particular, of course, mekso variables (lerfu strings) can be subscripted:

```✥13.1    li xy.boixici du li xy.boixipa su'i xy.boixire
the-number x-sub-3 equals the-number x-sub-1 plus x-sub-2
x3  = x1  + x2```

Subscripts always begin with the flag “xi” (of selma'o XI). “xi” may be followed by a number, a lerfu string, or a general mekso expression in parentheses:

```✥13.2    xy.boixino
x0

✥13.3 xy.boixiny.
xn

✥13.4 xy.boixi vei ny. su'i pa [ve'o]
xn+1}
```

Note that subscripts attached directly to lerfu words (variables) generally need a “boi” terminating the variable. Free modifiers, of which subscripts are one variety, generally require the explicit presence of an otherwise elidable terminator.

There is no standard way of handling superscripts (other than those used as exponents) or for subscripts or superscripts that come before the main expression. If necessary, further cmavo could be assigned to selma'o XI for these purposes.

The elidable terminator for a subscript is that for a general number or lerfu string, namely “boi”. By convention, a subscript following another subscript is taken to be a sub-subscript:

```✥13.5    xy.boi xi by.boi xi vo
xb4```

See ✥17.10 for the standard method of specifying multiple subscripts on a single object.

More information on the uses of subscripts may be found in Chapter 19.