| Optimal Threshold Control by the Robots of Web Search Engines with Obsolescence of Documents Recent countries visiting this post |  |
 | 8 | United States |
 | 4 | |
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| Optimal Threshold Control by the Robots of Web Search Engines with Obsolescence of Documents Recent countries visiting this post | |
| 8 | United States |
| 4 | |
| 3 | China |
| 1 | Germany |
| 1 | Italy |