// P92 (***) Von Koch's conjecture.
// Several years ago I met a mathematician who was intrigued by a problem
// for which he didn't know a solution. His name was Von Koch, and I don't
// know whether the problem has been solved since. [The "I" here refers to
// the author of the Prolog problems. ]
//
// d e-f 1 5-4 * *1*
// | | | | 6 2
// a-b-c -> 7-3-6 *4*3*
// | | 5
// g 2 *
//
// Anyway the puzzle goes like this: Given a tree with N nodes (and hence
// N-1 edges), find a way to enumerate the nodes from 1 to N and,
// accordingly, the edges from 1 to N-1 in such a way, that for each edge K
// the difference of its node numbers is equal to K. The conjecture is that
// this is always possible.
//
// For small trees the problem is easy to solve by hand. However, for
// larger trees, and 14 is already very large, it is extremely difficult to
// find a solution. And remember, we don't know for sure whether there is
// always a solution!
//
// Write a function that calculates a numbering scheme for a given tree.
// What is the solution for the larger tree pictured below?
//
// i g d-k p
// \| | |
// a-c-e-q-b
// /| | |
// h b f m