# Post's correspondence problem

(classic problem)

**Definition:**
Given a *set* of pairs of *strings*, find a sequence of pairs such that the concatenation of all first members of the pairs is the same string as the concatenation of all second members. This is an *undecidable problem*.

**Also known as** PCP.

Author: SKS

## More information

**Emil Post**, *A Variant of a Recursively Unsolvable Problem.* Bulletin of the American Mathematical Society, 52:264-268, 1946.

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Entry modified 14 April 2009.

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Cite this as:

Sandeep Kumar Shukla, "Post's correspondence problem", in
*Dictionary of Algorithms and Data Structures* [online], Vreda Pieterse and Paul E. Black, eds. 14 April 2009. (accessed TODAY)
Available from: https://www.nist.gov/dads/HTML/postsCorrespondProb.html