Ordinal sums, clockwise hackenbush, and domino shave

• Main Author: Carvalho, Alda
• Publication Date: 2020
• Other Authors: Huggan, Melissa A., Nowakowski, Richard, Santos, Carlos
• Format: Article
• Language: eng
• Source: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Download full: http://hdl.handle.net/10400.21/14829
• topic: Combinatorial game theory; Hackenbush; van Roode’s method; Ordinal sum

We present two rulesets, domino shave and clockwise hackenbush . The first is somehow natural and, as special cases, includes stirling shave and Hetyei’s Bernoulli game. Clockwise hackenbush seems artificial yet it is equivalent to domino shave. From the pictorial form of the game, and a knowledge of hackenbush, the decomposition into ordinal sums is immediate. The values of clockwise blue-red hackenbush are numbers and we provide an explicit formula for the ordinal sum of numbers where the literal form of the base is { x | } or { | x }, and x is a number. That formula generalizes van Roode’s signed binary number method for blue-red hackenbush.