You should read his paper showing that (under various unrealistic assumptions) travel planning is undecidable: http://www.demarcken.org/carl/papers/ITA-softwar

You should read his paper showing that (under various unrealistic assumptions) travel planning is undecidable: http://www.demarcken.org/carl/papers/ITA-software-travel-complexity/ITA-software-travel-complexity.pdf http://www.demarcken.org/carl/papers/ITA-software-travel-com...