This is a collection of short stories, and some of the best hard SF I've ever read. Egan has some excellent ideas, along with the scientific knowledge and writing skills to turn them into compelling stories. My favourite was the title story, in which researchers discover that they can manipulate inconsistencies in the universe's basic mathematical rules; "Reasons to be Cheerful", which explores the implications of being able to repair damage using neural prosthetics, came a close second. I'd recommend this unhesitatingly to anyone who likes SF.
ISBN 1857985737.