Update introduction.md

Author: mk-mxp

exercises/zebra-puzzle/introduction.md

@@ -10,6 +10,6 @@ However, only by combining the information in _all_ statements will you be able
 The Zebra Puzzle is a [Constraint satisfaction problem (CSP)][constraint-satisfaction-problem].
 In such a problem, you have a set of possible values and a set of constraints that limit which values are valid.
 Another well-known CSP is Sudoku.
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 [constraint-satisfaction-problem]: https://en.wikipedia.org/wiki/Constraint_satisfaction_problem
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