moral agents, probing deeply into the nature of human decision making and ethics." It cited some 450 sources, about 100 of which addressed major questions of machine ethics. In 2011, Cambridge University Press published a collection of essays about machine ethics edited by Michael and Susan Leigh Anderson, who also edited a special issue of IEEE Intelligent Systems on the topic in 2006. The collection consists of the challenges of adding ethical principles to machines. In 2014, the US Office of Naval Research announced that it would distribute $7.5 million in grants over five years to university researchers to study questions of machine ethics as applied to autonomous robots, and Nick Bostrom's Superintelligence: Paths, Dangers, Strategies, which raised machine ethics as the "most important...issue humanity has ever faced," reached #17 on the New York Times list of best selling science books. In 2016 the European Parliament published a paper, (22-page PDF), to encourage the Commission to address the issue of robots' legal status, as described more briefly in the press. This paper included sections regarding the legal liabilities of robots, in which the liabilities were argued as being proportional to the robots' level of autonomy. The paper also brought into question the number of jobs that could be replaced by AI robots. Definitions James H. Moor, one of the pioneering theoreticians in the field of computer ethics, defines four kinds of ethical robots. As an extensive researcher on the studies of philosophy of artificial intelligence, philosophy of mind, philosophy of science, and logic, Moor defines machines to be ethical impact agents, implicit ethical agents, explicit ethical agents, or full ethical agents. A machine can be more than one type of agent. Ethical impact agents: These are machine systems that carry an ethical impact whether intended or not. At the same time, these agents have the potential to act unethical. Moor gives a hypothetical example called the 'Goodman agent', named after philosopher Nelson Goodman. The Goodman agent compares dates but has the millennium bug. This bug resulted from programmers who represented dates with only the last two digits of the year. So any dates beyond 2000 would be misleadingly treated as earlier than those in the late twentieth century. Thus the Goodman agent was an ethical impact agent before 2000, and an unethical impact agent thereafter. Implicit ethical agents: For the consideration of human safety, these agents are programmed to have