The Asmiov-Clarke Treaty

I never knew this:

5.5 What is the Asimov-Clarke treaty?

The Asimov-Clarke Treaty of Park Avenue, put together as Asimov and Clarke
were travelling down Park Avenue in New York while sharing a cab ride,
stated that Asimov was required to insist that Arthur C. Clarke was the
best science fiction writer in the world (reserving second best for
himself), while Clarke was required to insist that Isaac Asimov was the
best science writer in the world (reserving second best for himself).
Thus the dedication in Clarke's book Report on Planet Three reads "In
accordance with the terms of the Clarke-Asimov treaty, the second-best
science writer dedicates this book to the second-best science-fiction
writer".

-- Isaac Asimov FAQ, via PC Authority.