Math just for fun; The Lady or the Tiger?, by Raymond Smullyan. New York: Alfred A. Knopf. 226 pp.

The initial chapters of Smullyan's second book on ''recreational'' logic and math problems offer brief logical riddles that are intended as a warm-up for bigger challenges to come.

After that, harder problems are strung together with a continuing plot line and characters.

The second half of the book is billed as the world's first ''mathematical novel.'' In it an inspector from Scotland Yard must deduce the combination of a very important safe, which leads him (and the reader) deep into real-life mathematical theory: the ''Incompleteness Theorem'' of Kurt Godel.