Turing test nothing of the real world." With these techniques, Weizenbaum's program was able to fool some people into believing that they were talking to a real person, with some subjects being "very hard to convince that ELIZA [...] is "not" human." Thus, ELIZA is claimed by some to be one of the programs (perhaps the first) able to pass the Turing test, even though this view is highly contentious (see below). Kenneth Colby created PARRY in 1972, a program described as "ELIZA with attitude". It attempted to model the behaviour of a paranoid schizophrenic, using a similar (if more advanced) approach
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,