## 18.7. Other useful selbri for mekso bridi

So far our examples have been isolated mekso (it is legal to have a bare mekso as a sentence in Lojban) and equation bridi involving
*du*. What about inequalities such as
“x < 5”? The answer is to use a bridi with an appropriate selbri, thus:

Here is a partial list of selbri useful in mathematical bridi:

Note the difference between
*dunli* and
*du*;
*dunli* has a third place that specifies the kind of equality that is meant.
*du* refers to actual identity, and can have any number of places:

Lojban bridi can have only one predicate, so the
*du* is not repeated.

Any of these selbri may usefully be prefixed with
*na*, the contradictory negation cmavo, to indicate that the relation is false:

As usual in Lojban, negated bridi say what is false, and do not say anything about what might be true.