Surprise birthday present problem (preliminary report): Abbreviated version

This paper presents a solution in a first-order monotonic logic to a simplified version of the Surprise Birthday Present Problem, a challenge problem for the formal commonsense reasoning community. The problem concerns two siblings who wish to surprise their sister with a present for her birthday: the aim is to construct a theory that will support the desired inferences, not allow undesired inferences, and be sufficiently elaboration tolerant to support reasoning about problem variations. The theory presented in this paper includes the development of a possible-worlds analysis of the concept of surprise, and an extension to previous work on multiple-agent planning to handle joint planning and actions. We show that this theory can solve the original SBP as well as many of its variants.