@inproceedings{Keel2009CONTRACTIBLEER,
title={CONTRACTIBLE EXTREMAL RAYS ON M0,n},
author={Se{\'a}n Keel and James F. Whidborne John McKernan},
year={2009}
}

One of the richest objects of study in higher dimensional algebraic geometry is the Mori-Kleiman (closed) cone of curves, N E 1 (M), defined as the closed convex cone in H 2 (M, R) generated by classes of irreducible curves on M. A lot of geometric information about M is encoded in the cone of curves. For example the possibilities for maps with connected fibres are determined by the cone's faces. Not surprisingly, N E 1 (M) is difficult to compute. Consider the problem of finding generators… CONTINUE READING