Solved cryptogram
No program can read another program and decide whether it will ever finish running.
Mathematics Facts, sourced to MacTutor History of Mathematics.
Or go to the puzzle’s own page first.
What it means
Turing proved this in 1936, before there were computers to run it on. Suppose such a checker existed. Wrap it in a program that asks the checker about itself and then does the opposite of the answer: it loops forever if the checker says it stops, and stops if the checker says it loops. Either answer is wrong, so no checker exists. This is why compilers warn about some infinite loops and can never catch all of them.
The claim comes from MacTutor History of Mathematics.
- SourceMacTutor History of Mathematics
- CollectionMathematics Facts
- Difficultyhard
- Length69 letters, 19 unique
Nearby in the collection
The facts either side of this one.
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