At Play With J  Answers to Problems for the Reader  In "At Play
With J", Edition 1, there were 4 questions left as exercises for
the reader. In Edition 2 we provide the answers in an Appendix.
The answers I've currently got are not necessarily the best.
However I'm not going to hold up publication of the book for
that reason. Instead the answers page in the book will carry a
link to this Wiki page, which will serve to coordinate a
leisurely discussion of answers.  If you wish to submit an
answer, or criticise or improve an existing answer, please do so
at the ends of the four papers concerned, viz. not on this
actual page. You will find answers already there.  From: Chapter
5: Jacobi's method [see midway down]  "Problem 1: Define a verb
which takes as argument a positive even integer n and yields a
permutation which, repeatedly applied to a conforming identity
permutation, produces, in successive pairs of items, all
possible choices of 2 items from n, with no duplications.
Problem 2: How many of the !n perm