Status of the SPARQL algebra

I've checked in my working copy of a proposed SPARQL algebra.

http://www.w3.org/2001/sw/DataAccess/rq23/rq24-algebra.html

It is not finished.  You can help.

The most useful comments to me at this stage are one of the form:

1/ Comments on the structure
2/ Ways to improve the expression of ideas
3/ Proposed content (xhtml or text) for the document
4/ Advice on how to typeset squiggly symbols in portable XHTML,
    What is the state of the art?
    At the moment I've written words so I concentrate on the content.

	Andy