Penguins can make cake

This article is a reply to Matthew Ginsberg's article entitled Universal Planning: An (Almost) Universally Bad Idea. Ginsberg argues that uni-versal plans are infeasible for reasons of compu-tational complexity and concludes that classical planning -- or something like it -- is the appropri-ate basis for activity. He also argues that a number of other systems, including Pengi, are approximately universal plans and subject to the same criticisms. I think that this extension is incorrect. I illustrate my reasoning with a description of Blockhead, a Pengi-like system that efficiently solves the fruitcake problem which Ginsberg argues is infeasible for universal plans. The structure of Blockhead elucidates the relationship between planning, universal plans, and Pengi. I conclude that planning and universal plans are computationally intractable because of the representational assumptions they make.