| Clue | Source | Date |
|---|---|---|
| David ____'s list of 23 problems, published in 1902, kept mathematicians busy for much of the 20th century | The Times Specialist Sunday | 21 May 2023 |
| David --, German mathematician (1862-1943) | The Telegraph General Knowledge | 14 Sep 2020 |
| German mathematician, curiously blithe about arithmetic? |