PALATINE, Ill. — Arthur C. Clarke's health was failing fast, but he still had a story to tell. So he turned to fellow science fiction writer Frederik Pohl, and together the longtime friends wrote what turned out to be Clarke's last novel.

"The Last Theorem," which grew from 100 pages of notes scribbled by Clarke, is more than a futuristic tale about a mathematician who discovers a proof to a centuries-old mathematical puzzle.

The novel, released Tuesday, represents a historic collaboration between two of the genre's most influential writers in the twilight of their careers. Clarke, best known for his 1968 work, "2001: A Space Odyssey," died in March at age 90; Pohl is 89.

"As much as anything, it'll be a historic artifact," says Robin Wayne Bailey, a former president of Science Fiction Writers of America and a writer. "This is a book between two of the last remaining giants in the field."

Clarke originally intended "The Last Theorem" to be his last solo project, and he began writing it in 2002.

But progress was slow because of his poor health, and he missed the book's original 2005 publication deadline. Worried the book wouldn't be published at all, he began to search for a co-author.

While the search was under way, Clarke would often tell his aides, "I hope 'The Last Theorem' won't become the lost theorem!" Nalaka Gunawardene, one of Clarke's aides in Sri Lanka, said.

Pohl said he volunteered for the job and set about making sense of 100 pages of notes Clarke left him. About 40 or 50 pages of scenes were fully written, but the rest contained only undeveloped ideas. On some pages, there were only one or two lines of text, he said.

AUTHORS' PROPHECIES

"The Last Theorem" includes a weapon called Silent Thunder that neutralizes all electronic activity in a given area to harmlessly disarm entire nations. Another is the space elevator, a cord suspended from an orbiting object in space that can pull objects from Earth, rather than rely on rocket power to launch them.

Pohl said his research and conversations with friends who are scientists convince him both will one day exist.

"If we can somehow figure out what possible futures there might be," he said, "you can try to encourage the ones you like and avoid the ones you don't."