SCIENCE: Thin high cloud?

Questions

- Invertible counterpoint in which three parts can be interchanged, each making a suitable bass for the other.?

- The playing of three notes simultaneously on a stringed instrument by the placing of the left hand fingers on the strings and shortening the vibrating length.?

- A group of three notes played in the time of 2.?

- Time consisting of three beats to the bar (e.g. 3 / 4, 3 / 2, 3 / 8).?

- The rapid articulation of T-K-T on a wind instrument. This is difficult to do on reed instruments.?