A $n$-dimensional algebraic $k$-variety $M$ is **rational** if there is a birational map $M\to P^n_k$ to the projective space. A variety is irrational if it is not rational. It is often a difficult question wheather some concrete example of a variety is rational.

Last revised on May 19, 2010 at 18:27:58. See the history of this page for a list of all contributions to it.