Answer: You wouldn't be just pulling my chain, would you? I have a feeling you're handing me your assigned essay topic. Those would be Bartok's Six Dances in Bulgarian Rhythm - how about if I just talk a little about Bulgarian Rhythm, which may be of more general interest?

"Bulgarian rhythm" is the use of asymmetrical rhythm groups within measures, particularly in a fast tempo. In Bartok's own words, "'Bulgarian' rhythm comes about when very quick rhythmic values (MM 300-400 or more) are grouped asymmetrically thus, e.g. such as 4+2+3 (and not 3+3+3!)."

Bartok sometimes indicates the irregular grouping by using an "additive time signature" for example, 4+2+3 /16 instead of 9/16. But an additive signature is not essential to Bulgarian rhythm. For example, the meter signature could be 9/16 grouped as above, or 8/16 with the notes grouped as 3 + 3 + 2 instead of the expected two groups of 4 (see below for an example).

What is "very quick"? The typical meter for Bulgarian rhythm is based on 16ths, and it is the 16ths that Bartok is referring to as moving at a metronome speed of 300 to 400. He also likes 8ths as a basic unit, but if the meter signature is based on 16ths you could set the quarter note speed to between 90 and 100 in our software to get the 16ths speed he's recommending.

An old friend of mine is a Bulgarian and I am assured that though he is not personally asymmetrical, this rhythmic device is not misnamed; it really does derive from traditional music in that country. You hear it in popular tunes like Shto Mi E Milo, whose tune has the pattern 3 + 3 + 2 and could be notated like this:

It's a charming sound, jagged and surprising (double-click the image of the music to hear it).