# 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.

Go to the
Dictionary of Algorithms and Data
Structures home page.

If you have suggestions, corrections, or comments, please get in touch
with Paul Black.

Entry modified 21 December 2020.

HTML page formatted Mon Dec 21 09:49:05 2020.

Cite this as:

Sandeep Kumar Shukla, "Post's correspondence problem", in
*Dictionary of Algorithms and Data Structures* [online], Paul E. Black, ed. 21 December 2020. (accessed TODAY)
Available from: https://www.nist.gov/dads/HTML/postsCorrespondProb.html