Eliding NU rafsi involves the same restrictions as eliding SE rafsi, plus additional ones. In general, NU rafsi should not be elided from the tertau, since that changes the kind of thing the lujvo is talking about from an abstraction to a concrete sumti. However, they may be elided from the seltau if no reasonable ambiguity would result.

A major difference, however, between SE elision and NU elision is that the former is a rather sparse process, providing a few convenient shortenings. Eliding nu, however, is extremely important in producing a class of lujvo called “implicit-abstraction lujvo”.

Let us make a detailed analysis of the lujvo nunctikezgau, meaning “to feed”. (If you think this lujvo is excessively longwinded, be patient.) The veljvo of nunctikezgau is nu citka kei gasnu. The relevant place structures are:

In accordance with the procedure for analyzing three-part lujvo given in Section 12.8, we will first create an intermediate lujvo, nuncti, whose veljvo is nu citka [kei]. By the rules given in Section 12.12, nuncti has the place structure

Now we can transform the veljvo of nunctikezgau into nuncti gasnu. The g2 place (what is brought about by the actor g1) obviously denotes the same thing as n1 (the event of eating). So we can eliminate g2 as redundant, leaving us with a tentative place structure of

But it is also possible to omit the n1 place itself! The n1 place describes the event brought about; an event in Lojban is described as a bridi, by a selbri and its sumti; the selbri is already known (it's the seltau), and the sumti are also already known (they're in the lujvo place structure). So n1 would not give us any information we didn't already know. In fact, the n1=g2 place is dependent on c1 and c2 jointly – it does not depend on either c1 or c2 by itself. Being dependent and derived from the seltau, it is omissible. So the final place structure of nunctikezgau is:

There is one further step that can be taken. As we have already seen with balsoi in Section 12.5, the interpretation of lujvo is constrained by the semantics of gismu and of their sumti places. Now, any asymmetrical lujvo with gasnu as its tertau will involve an event abstraction either implicitly or explicitly, since that is how the g2 place of gasnu is defined.

Therefore, if we assume that nu is the type of abstraction one would expect to be a se gasnu, then the rafsi nun and kez in nunctikezgau are only telling us what we would already have guessed – that the seltau of a gasnu lujvo is an event. If we drop these rafsi out, and use instead the shorter lujvo ctigau, rejecting its symmetrical interpretation (“someone who both does and eats”; “an eating doer”), we can still deduce that the seltau refers to an event.

(You can't “do an eater”/ gasnu lo citka, with the meaning of do as “bring about an event”; so the seltau must refer to an event, nu citka. The English slang meanings of “do someone”, namely “socialize with someone” and “have sex with someone”, are not relevant to gasnu.)

So we can simply use ctigau with the same place structure as nunctikezgau:

This particular kind of asymmetrical lujvo, in which the seltau serves as the selbri of an abstraction which is a place of the tertau, is called an implicit-abstraction lujvo, because one deduces the presence of an abstraction which is unexpressed (implicit).

To give another example: the gismu basti, whose place structure is

can form the lujvo basygau, with the place structure:

where both basti and basygau are translated “replace” in English, but represent different relations: basti may be used with no mention of any agent doing the replacing.

In addition, gasnu-based lujvo can be built from what we would consider nouns or adjectives in English. In Lojban, everything is a predicate, so adjectives, nouns and verbs are all treated in the same way. This is consistent with the use of similar causative affixes in other languages. For example, the gismu litki, meaning “liquid”, with the place structure

can give likygau, meaning “to liquefy”:

While likygau correctly represents “causes to be a liquid”, a different lujvo based on galfi (meaning “modify”) may be more appropriate for “causes to become a liquid”. On the other hand, fetsygau is potentially confusing, because it could mean “agent in the event of something becoming female” (the implicit-abstraction interpretation) or simply “female agent” (the parallel interpretation), so using implicit-abstraction lujvo is always accompanied with some risk of being misunderstood.

Many other Lojban gismu have places for event abstractions, and therefore are good candidates for the tertau of an implicit-abstraction lujvo. For example, lujvo based on rinka, with its place structure

are closely related to those based on gasnu. However, rinka is less generally useful than gasnu, because its r1 place is another event rather than a person: lo rinka is a cause, not a causer. Thus the place structure of likyri'a, a lujvo analogous to likygau, is

and would be useful in translating sentences like “The heat of the sun liquefied the block of ice.”

Implicit-abstraction lujvo are a powerful means in the language of rendering quite verbose bridi into succinct and manageable concepts, and increasing the expressive power of the language.