Published online by Cambridge University Press: 01 August 1999
We give a negative answer to the question of whether every partial combinatory algebra can be completed. The explicit counterexample will be an intricately constructed term model. The construction and the proof that it works depend heavily on syntactic techniques. In particular, it provides a nice example of reasoning with elementary diagrams and descendants. We also include a domain-theoretic proof of the existence of an incompletable partial combinatory algebra.