Reverse Turing test subject of the test involves reversing the roles of the real and control subjects. When a Turing test is applied to a mixed group of human and computer subjects, the computers are the nominal subjects. However, the humans are judged in exactly the same way, and so their Turing test scores can also be calculated. This is another way of viewing the situation described in the previous section. The term "reverse Turing test" has also been applied to a Turing test (test of humanity) that is administered by a computer. In other words, a computer administers a test to determine
Turing completeness it is impossible to determine whether this characteristic will hold. This impossibility poses problems when analyzing real-world computer programs. For example, one cannot write a tool that entirely protects programmers from writing infinite loops, or protects users from supplying input that would cause infinite loops. One can instead limit a program to executing only for a fixed period of time (timeout), or limit the power of flow control instructions (for example, providing only loops that iterate over the items of an existing array). However, another theorem shows that there are problems solvable by Turing-complete languages that cannot be solved by