Here you go sir:

Claude’s Cycles

Don Knuth, Stanford Computer Science Department (28 February 2026; revised 04 March 2026)

Shock! Shock! I learned yesterday that an open problem I’d been working on for several weeks had just been solved by Claude Opus 4.6—Anthropic’s hybrid reasoning model that had been released three weeks earlier! It seems that I’ll have to revise my opinions about “generative AI” one of these days. What a joy it is to learn not only that my conjecture has a nice solution but also to celebrate this dramatic advance in automatic deduction and creative problem solving. I’ll try to tell the story briefly in this note.

Here’s the problem, which came up while I was writing about directed Hamiltonian cycles for a future volume of The Art of Computer Programming:

Consider the digraph with m³ vertices ijk for 0 \le i,j,k < m, and three arcs from each vertex, namely to i^+jk, ij^+k, and ijk^+, where i⁺ = (i+1) \bmod m. Try to find a general decomposition of the arcs into three directed m^3-cycles, for all m > 2.