New paper about Worlds

Here's the link: http://www.vpri.org/pdf/tr2010001_worlds.pdf

And here's what's new compared to Chapter 4 of my dissertation:

a better semantics for the commit operation — it now includes a serializability check that makes programming with worlds much safer/saner,

a new section that describes a more efficient, Squeak-based implementation, and

a neat case study that shows that our new implementation is fast enough to do interesting things with worlds.