As the research in multi-agent domain continues to grow it is becoming more and more important to investigate the agents’ relations in such systems: not only to reason about agents’ perception of the world but also about agents’ knowledge of her and others’ knowledge. This type of study is referred as epistemic reasoning. In certain domains, e.g., economy, security, justice and politics, reasoning about others’ beliefs could lead to winning strategies or help in changing a group of agents’ view of the world. In this work we formalize the epistemic planning problem where the state description is based on non-well-founded set theory. The introduction of such semantics would permit to characterize the planning problem in terms of set operations and not in term of reachability, as the state-of-the-art suggests. Doing so we hope to introduce a more clear semantics and to establish the basis to exploit properties of set based operations inside multi-agent epistemic planning. © 2019 CEUR-WS. All rights reserved.