'anu' is both a conjunction, "or", and interrogative "which of?" The difference in print is the presence or absence of a question mark at the end (what it is in speech is unclear). As an interrogative, it frames choice questions 'x anu y?'. It is usually said that there are two proper answers to such a question, 'x' and 'y'. But, in general, there are actually four. To be sure, one or both of the additions answers may be excluded by circumstances: contradiction, prohibitions, etc., but, in the absence of these they remain. The two additional answers are, of course, "both" and "neither". "both" may be excluded by a mother saying you can't choose cake and ice cream as well as contradictions, like the choice of life or death. "neither" may be excluded by the choices being exhaustive (life or death again) or by external restrictions (You vill take coffee or tea!). It should be noted that, at a crucial point, tp doesn't have good words for either of these alternatives, though 'en' might work for "both" or "en kin" to stress it as a correction to 'anu'.
All this is significant because of a problem with 'ala', negation. There are several kinds of negations, but are present concern is with the main ones, internal (contrary, predicate) and external (contradictory, sentential) negation. Internal negation attaches to a word to create a new expression which refers to all the things the original word does not refer to (usually practically confined to things "of the appropriate sort"). So, for example, 'soweli ala' refers to all things that are not soweli (presumably all living things with maybe even further restrictions implicit) and 'loje ala' refers to all colors (I suppose) other than red. External negation attaches to a sentence is creates a sentence that says that the original sentence is false, that directly denies the original sentence.
In tp, 'ala' is officially defined as an internal negation, naming the complement class. So, 'soweli li lon ala supa',which often presented as the (external) negation of a sentence, doesn't, in fact, deny 'soweli li lon supa', but rather asserts another claim incompatible with it, that soweli is in the class of things which don't bear the lon-ness relation to supa. Of course, they generally amount to the same thing, true in the same circumstances.
But not always. Consider 'jan ali li kama' and 'jan ali li kama ala'. The first says that everybody is in the class of comers. The second says that everyone is in the class of non-comers, i.e., "Everybody came" and "Nobody came" and the latter is clearly much more than a denial of the first. Given a choice between these two, in the so-called yes/no question 'jan ali li kama ala kama?', neither pick will work if some came and some didn't. Yet those are the only choices allowed. Apparently. But the 'x ala x' is an version of 'x ala anu x', a choice question, so the answer "neither" (however that may be said in tp -- obviously not 'ala') is available and proper.
Of course, we could save the situation in another way, which would keep the current story about 'x ala x'. This would be to take 'ala', at least immediately after the verb, as a sentential negation. So 'jan ali li kama ala' would be the denial of 'jan ali li kama', not "Nobody came" but "Not everybody came". But this reading of 'ala' turns up in other places as well, even in the official interpretations. 'jan ala li kama' is never read as "Some non-human came", as the official interpretation requires, but as "Nobody came", more in line with the sentential reading, though not perfectly, since that is 'jan li kama ala', which is usually not used in that way. The rules (if there are any) seem to involved the interplay of 'ala' with 'ali' and perhaps the implicit particular quantifier in bare noun forms ('jan ala' is parallel to 'jan ali ala' "not everybody"). Clearly, following either rule too rigorously will lead to trouble and context may not always decide the right way out.
There are two other negations which play some role in useful speech. One is the strong form of internal negation, which gives not just the complement class but the opposite class along some linguistically vague dimension. There are obvious cases like "good" and "evil" and possibly "red" and "green", but for many concepts the polar opposite is difficult to find or define. What is the opposite of "lizard", say? There is one class that is particularly interesting and that is in the verbs of process and achievement. Achievements (in the aspect sense) have mirror images: starting and stopping, for example. Processes have retroprocesses, building up and tearing down, advancing and retreating. It is hard to work out contexts where these are clearly distinct from the simple internal negation, how tearing a building down is distinct, linguistically, from not building it at all: both would be 'tomo ala', say. But there may be occasions when the notion is useful.
The other negation that has a role to play is presupposition negation. It is mainly for answering loaded questions, but can also be a shorthand for simply denying the assumptions some has made, even if they have not asked a question based on them. In the question case, answering the question either "yes" or "no" (or filling in the blank) amounts to admitting the presuppositions: I doesn't matter whether the question is "Have you stopped beating your wife?" or "When did you stop beating your wife?" Again, as in the 'x ala x' situation, a mere 'ala' is inadequate, but there is not idiom yet to hand to deal with the issue.
So, here are some problems in search of good tp solutions: a word for "neither" (and maybe"both"), a rule for telling internal from external negations (or a way to get everyone to follow one pattern consistently), a word fr polar negation and especially retroprocessing, and a metanegation fr rejecting presuppositions efficiently. Have fun.