V.V. Shokurov has written several papers over the course of about 10 years which are called "Letters of a bi-rationalist". Here are the ones that I could find:
- Letters of a bi-rationalist. I. A projectivity criterion
- On rational connectedness (this is letter number 2, as you can see from the first line in the text)
- Letters of a bi-rationalist. IV. Geometry of log flips
- Letters of a bi-rationalist V: Mld's and termination of log flips
- Letters of a bi-rationalist. VII. Ordered termination
The question is: what happened to the letters number III and VI?