U is a Zen conlang invented by a conlanger arseniiv in 2013.
Phonemic inventory of U consists of a single phoneme /u/, that has all possible implementations by virtue of the non-existence of minimal pairs.
Lexicon of U consists of one word u /u/ meaning it's pointless, it's nonsense, it's not necessary, it does not exist, ⊥. The repetition of the word, as well as its absence does not affect the meaning.
U uses phonetic writing. Anything written can be considered as /u/.
You can not determine whether an inscription is written in U or not in U, you cannot say whether your friend said to you something in U or not in U, so that's why is it and that's why isn't it u? Anyway, u.
U seems to be the conlang most completely described among others in its grammar, phonetics, usage and semantics.
- http://arseniiv.info/2015/11/u-zen-conlang/ (in Russian)
- http://lingvoforum.net/index.php/topic,61351.0.html (in Russian)