links: http://www.tau.ac.il/~nogaa/PDFS/amsz4.pdf http://www.cs.dartmouth.edu/~ac/Teach/CS85-Fall09/Notes/lecnotes.pdf http://polylogblog.wordpress.com/2009/09/27/bite-sized-stream-ams-sketching/ http://www.tcs.tifr.res.in/~workshop/bhu_igga/bhu-talk.pdf