What are the two forms of improvisation?

* Through-composed improvisation: In this type of improvisation, the performer creates the music as they go along, without any predetermined plan. This can be done by using a variety of techniques, such as:

* Call and response: One performer plays a phrase or melody, and the other performer responds with a similar phrase or melody.

* Trading fours: Two performers take turns playing solos for four measures each.

* Coltrane changes: A performer plays a series of rapid chord changes, and the other performer improvises over the changes.

* Head arrangement: In this type of improvisation, the performer creates a new arrangement of a pre-existing piece of music. This can be done by changing the melody, harmony, or rhythm of the original piece.