What are pro-sumti and pro-bridi? What are they for?

To Speak Of Many Things: The Lojban sumti

### 15. Number summary

The sumti which refer to numbers consist of the cmavo “li” (of selma'o LI) followed by an arbitrary Lojban mekso, or mathematical expression. This can be anything from a simple number up to the most complicated combination of numbers, variables, operators, and so on. Much more information on numbers is given in Chapter 18. Here are a few examples of increasing complexity:

15.1) li vo
the-number four
4
15.2) li re su'i re
the-number two plus two
2 + 2
15.3) li .abu bopi'i xy. bote'a re su'i by. bopi'i xy. su'i cy.
the-number a times x to-power 2 plus b times x plus c
ax^{2} + bx + c

An alternative to “li” is “me'o”, also of selma'o LI. Number expressions beginning with “me'o” refer to the actual expression, rather than its value. Thus Example 15.1 and Example 15.2 above have the same meaning, the number four, whereas

15.4) me'o vo
the-expression four
“4”

and
15.5) me'o re su'i re
the-expression two plus two
“2+2”

refer to different pieces of text.
The implicit quantifier for numbers and mathematical expressions is “su'o”, because these sumti are analogous to “lo” descriptions: they refer to things which actually are numbers or pieces of text. In the case of numbers (with “li”), this is a distinction without a difference, as there is only one number which is 4; but there are many texts “4”, as many as there are documents in which that numeral appears.

What are pro-sumti and pro-bridi? What are they for?

To Speak Of Many Things: The Lojban sumti