WHY DOESN'T GLOSA HAVE DIFFERENT DEFINITE AND INDEFINITE ARTICLES?
Short answer: Glosa really doesn't have articles. U(N)/PLU is really a NOUN INDICATOR, showing that a noun is soon following. It happens to behave somewhat as an article does. It helps to distinguish nouns from verbs.
Every language has different ways of expressing "definiteness." You will find different uses of articles among different languages and even in English itself.
The definite article means: "You and I both know what I'm referring to." If the person you are speaking to knows a man came to your door yesterday, you would say to that person:
THE man who came to my door....
If a second person you are talking to doesn't know anyone came to your door, you would say:
A man who came to my door....
A and THE in the examples above refer to the same man. So just how definite is the definite article? The definite article is not definite enough for many legal situations. That's why lawyers resort to saying things like "the party of the first part."
There are some languages that have no articles. Russian is an example of this. Because Russian has no definite article, translators while negotiating the SALT Treaties constantly had to ask, "Which country? Which missiles?" The only reason the Soviet Union signed the treaty in the end was because they thought it had something to do with spice--
Of course not! Russians, however, who are learning to speak English often omit articles. One once told me, "Why use article? Is not necessary!" I understood her just fine.
While we English speakers often talk about freedom, brotherhood, and equality, the French talk about "THE freedom," "THE brotherhood," and "THE equality." Germans refer to "THE Switzerland" and "THE Turkey." In England you go "to hospital"; in the US you go "to THE hospital." English also has a habit of using possessive adjectives (MY, YOUR, HIS, HER, OUR, THEIR) where many other languages use articles.
So Glosa has this simple rule: If there is one thing, write U or UN in front of it; if there is more than one thing, write PLU in front of it. And, as I told my daughters when I was teaching them Glosa, if you don't know how many-- skip it. Think carefully about how you use U(N)/PLU and expect to see variations in how others use this.
If after all this you still feel you need a way to express the English article, just say what it MEANS:
The man you and I know came to the door.
Un andro; tu e mi ski, pa veni a porta.
A man I know, but you don't, came to the door.
Un andro; mi ski, sed tu ne ski, pa veni a porta.