## 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:

Example 18.38.

 li xy. mleca li mu The-number x is-less-than the-number 5.

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

 x1 is identical to x2, x3, x4, ... x1 is equal/congruent to x2 in/on property/quality/dimension/quantity x3 x1 is less than x2 x1 is greater than x2 x1 is less than or equal to x2 [du ja mleca, equal or less] x1 is greater than or equal to x2 [du ja zmadu, equal or greater] x1 is similar to x2 [tarmi dunli, shape-equal] turdu'i x1 is isomorphic to x2 [stura dunli, structure-equal] x1 is a member of set x2 gripau x1 is a subset of set x2 [girzu pagbu, set-part] x1 is approximately equal to x2 [namcu jibni, number-near] terci'e x1 is a component with function x2 of system x3

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:

Example 18.39.

 py. du xy.boi zy. “p” is-identical-to “x” “z” p = x = z

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:

Example 18.40.

 li re su'i re na du li mu the-number 2 + 2 is-not equal-to the-number 5. 2 + 2 ≠ 5

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