{"type":"ScholarlyArticle","title":"Why Can’t You Do That HAL? Explaining Unsolvability of Planning Tasks","authors":[{"name":"Sarath Sreedharan","slug":"sarath-sreedharan","given":"Sarath","family":"Sreedharan","affiliation":"CIDSE , Arizona State University , Tempe , AZ 85281 USA"},{"name":"Siddharth Srivastava","slug":"siddharth-srivastava","given":"Siddharth","family":"Srivastava","affiliation":"CIDSE , Arizona State University , Tempe , AZ 85281 USA"},{"name":"David Smith","slug":"david-smith","given":"David","family":"Smith","affiliation":"PSresearch"},{"name":"Subbarao Kambhampati","slug":"subbarao-kambhampati","given":"Subbarao","family":"Kambhampati","affiliation":"CIDSE , Arizona State University , Tempe , AZ 85281 USA"}],"abstract":"Explainable planning is widely accepted as a prerequisite for autonomous agents to successfully work with humans. While there has been a lot of research on generating explanations of solutions to planning problems, explaining the absence of solutions remains an open and under-studied problem, even though such situations can be the hardest to understand or debug. In this paper, we show that hierarchical abstractions can be used to efficiently generate reasons for unsolvability of planning problems. In contrast to related work on computing certificates of unsolvability, we show that these methods can generate compact, human-understandable reasons for unsolvability. Empirical analysis and user studies show the validity of our methods  as well as their computational efficacy on a number of benchmark planning domains.","doi":"10.24963/ijcai.2019/197","url":"https://ijcai.org/proceedings/2019/197","pdf":"https://ijcai.org/proceedings/2019/0197.pdf","markdown":"https://ijcai.org/proceedings/2019/197.md","bibtex":"https://ijcai.org/proceedings/2019/bibtex/197","volume":{"slug":"2019","title":"Proceedings of the Twenty-Eighth International Joint Conference on Artificial Intelligence","short_title":"IJCAI 2019","url":"https://ijcai.org/proceedings/2019/","year":2019,"location":"Macao","dates":"10-16 August 2019","editors":"Sarit Kraus","isbn":"978-0-9992411-4-1","publisher":"International Joint Conferences on Artificial Intelligence Organization","doi_prefix":"10.24963/ijcai.2019"},"section":"Humans and AI","track":"Main track","number":197,"pages":{"first":1422,"last":1430},"keywords":["Humans and AI: Human-AI Collaboration","Agent-based and Multi-agent Systems: Human-Agent Interaction"],"videos":[],"references":[{"position":1,"raw":"[Bacchus and Kabanza, 2000] Bacchus, F., and Kabanza, F. 2000. 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