| skos:altLabel | - problems
- unsolved problems
- 14th problem of Hilbert
- 22 other unsolved problems of the 19th century
- 23 challenges
- 23 problems
- 23 problems posed by Hilbert in 1900
- 23 unsolved mathematical problems
- 23 unsolved problems
- 23 unsolved problems in mathematics
- Hilbert Problems
- Hilbert's 23 problems
- Hilbert's cancelled 24th problem
- Hilbert's list
- Hilbert's list of mathematical problems
- Hilbert's twenty three problems
- Hilbert's well-known 23 problems
- collection of problems
- famous problems
- fundamental problems
- his list of 23 problems
- his list of 23 problems in mathematics
- list of 23 problems
- list of important open questions
- list of mathematical problems
- list of open mathematical problems
- mathematical problems
- twelfth problem
- twenty three unsolved problems of mathematics
- twenty-three open problems
- twenty-three problems
- twenty-three then unsolved problems
- twenty-three unsolved problems
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