 Krause also developed an intense collaboration with Steven French to develop a concept of individuality for the quantum ontology (Krause and French 1995, 2007; French and Krause 1995, 1999, 2003); they also advanced some ideas about individuality in quantum field theory (French and Krause 2010). This collaboration gave rise to a very relevant book on the matter (French and Krause 2006), which discusses the problem of individuality in philosophy and in classical and quantum physics and articulates quasi-set theory as a theory for non-individuals.