| __Felix On-line__ *(Site not responding. Last check: 2007-10-17)* |

| | Much of the **mathematical** research in the 20th century has been influenced by this list of **unsolved** **problems**, as both successful and unsuccessful attempts at solutions have yielded a number of important discoveries on the way. |

| | The list of **problems** itself has been carefully selected to include not only the most difficult ones, but also the ones whose solutions would have a relevance to areas of mathe-matics and the other sciences beyond the one in which the **problem** was originally for-mulated, hopefully leading to further serendipitous discoveries en route. |

| | Generally speaking, **problems** that are in P are easy to solve, while **problems** in NP are difficult to solve, but significantly, given an answer to an NP **problem**, it is easy to verify whether it is indeed a solution. |

| www.felixonline.co.uk /2002-04/article.php?aid=1988 (1464 words) |