Reverse Turing test a computer is then said to "pass the Turing test" if it is also judged human. Any of these roles may be changed to form a "reverse Turing test". Arguably the standard form of the reverse Turing test is one in which the subjects attempt to appear to be a computer rather than a human. A formal reverse Turing test follows the same format as a Turing test. Human subjects attempt to imitate the conversational style of a conversation program such as ELIZA. Doing this well involves deliberately ignoring, to some degree, the meaning of the conversation that is immediately
Turing completeness is that there exist problems for which it is impossible to predict what a (Turing-complete) system will do over an arbitrarily long time. The classic example is the halting problem: create an algorithm which takes as input (a) a program in some Turing-complete language, and (b) some data to be fed to "that" program; and which determines whether the program, operating on the input, will eventually stop or will continue forever. It is trivial to create an algorithm that can do this for "some" inputs, but impossible to do this in general. For any characteristic of the program's eventual output,