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Fengkui Ju

Possible papers associated with this exact author name in Arrow. This page groups case-insensitive exact name matches and is not a full identity disambiguation profile.

8 papers

2 author rows

I&C Journal 2026 Journal Article

Generalized alternating-time temporal logics I: Semantics

Fengkui Ju
Thomas Ågotnes
Yinfeng Li
Emiliano Lorini

Alternating-time Temporal Logic ATL is a key framework for reasoning about strategic and coalitional ability. Built into standard ATL are several assumptions, including neverending interaction (the system never stops), joint action determinism (the next state is uniquely determined by the current state and actions chosen by all agents) and independence of choices (an agent’s choice does not depend on choices of other agents). Recently, combinations of these assumptions have been relaxed in the case of Coalition Logic – the next time fragment of ATL – resulting in eight different logics. In this paper we do the same for full ATL. We define a generalized semantics and prove some key semantic properties, laying the groundwork for axiomatic completeness. Along the way, we provide proofs of some semantic properties of standard ATL that are currently missing in the literature. In particular, we show that the interpretations based on positional and historical strategies are equivalent, in the general setting. This is “well known” for standard ATL, but perhaps surprisingly, it turns out that there is no proof of it in the literature. We also show that the semantics based on strategies and co-strategies are equivalent. All of this hinges on a fixed point characterization of “globally” and “until”, which we provide (the latter case is missing even for full ATL in the literature).

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I&C Journal 2026 Journal Article

Seven kinds of equivalent models for generalized coalition logics

Zixuan Chen
Fengkui Ju

Coalition Logic is an important logic in the logical study of strategic reasoning. It admits two kinds of semantics: one based on concurrent game models, and the other based on alpha neighborhood models, which capture the alpha powers of coalitions. In two recent papers, Li and Ju argued that, generally, concurrent game models have three assumptions that are too strong: seriality, independence of agents, and determinism. They presented eight coalition logics based on eight classes of general concurrent game models determined by which of the three assumptions are met. In this paper, we show that the set of valid formulas of each of these eight logics can equivalently be characterized by six alternative classes of models, each of which provides a natural and well-motivated representation of coalitional powers: (1) single-coalition-first action models, in which the outcome functions for single coalitions determine the outcome functions for all other coalitions; (2) single-coalition-first actual neighborhood models, in which the neighborhood functions for single coalitions determine the neighborhood functions for all other coalitions; (3) clear grand-coalition-first action models, in which the outcome function for the grand coalition determines the outcome functions for all other coalitions, and distinct joint actions of the grand coalition yield distinct outcomes; (4) clear single-coalition-first actual neighborhood models, in which the actual powers of single coalitions are pairwise disjoint; (5) tree-like grand-coalition-first action models, in which every state has a unique history; and (6) tree-like single-coalition-first actual neighborhood models, in which every state also has a unique history.

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LORI Conference 2025 Conference Paper

Next-Time Coalition Logic

Thomas Ågotnes
Fengkui Ju

Abstract Coalition Logic (CL) can be seen as the next-time fragment of Alternating-time Temporal Logic (ATL). Modalities in ATL are combinations of strategy quantifiers and tense modalities “glued” together. In ATL* this requirement is relaxed, and the two types of modalities can be mixed freely, resulting in more expressive logics. That comes at a cost: for example, as far as we know, no complete axiomatisation of ATL* exists. In this paper we study the next-time fragment of ATL*: CL*. Like in ATL and unlike in CL, we must now consider strategies rather than just actions, and like in ATL* but unlike in ATL, it matters whether we use full-memory or just memoryless strategies. The question of whether CL* actually is more expressive than CL hinges on that choice. We characterise the relative expressive power of the two variants of CL* compared to CL, and give a sound and complete axiomatisation of CL* with full-memory strategies.

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LORI Conference 2019 Conference Paper

Towards a Logic for Conditional Local Strategic Reasoning

Valentin Goranko
Fengkui Ju

Abstract We consider systems of rational agents who act in pursuit of their individual and collective objectives and we study the reasoning of an agent or an external observer about the consequences from the expected choices of action of the other agents based on their objectives, in order to assess the reasoner’s ability to achieve his own objective. To formalize such reasoning we introduce new modal operators of conditional strategic reasoning and use them to extend Coalition Logic in order to capture variations of conditional strategic reasoning. We provide formal semantics for the new conditional strategic operators, introduce the matching notion of bisimulation for each of them and discuss and compare briefly their expressiveness.

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LORI Conference 2017 Conference Paper

A Dynamic Approach to Temporal Normative Logic

Fengkui Ju
Gianluca Grilletti

Abstract State commands refer to states, not actions. They have a temporal dimension explicitly or implicitly. They indirectly change what we are permitted, forbidden or obligated to do. This paper presents \({{\mathrm{\mathsf {DTNL}}}}{}\), a deontic logic meant to handle state commands based on the branching-time temporal logic \(\mathsf {PCTL}^*\). The models of \({{\mathrm{\mathsf {DTNL}}}}{}\) are trees with bad states, which are identified by a propositional constant \(\mathfrak {b}\) introduced in the language. To model state commands, a dynamic operator that adds states to the extension of \(\mathfrak {b}\) is introduced.

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LORI Conference 2015 Conference Paper

Trace Semantics for IPDL

Fengkui Ju
Nana Cui
Shujiao Li

Abstract Other than relation semantics, IPDL, the extension of PDL with intersection of actions, has a natural trace semantics where the interpretation of an action is a set of sequences of states. IPDL in trace semantics can describe paced concurrent games very well. Surprisingly, IPDL can be reduced to a sublanguage of it in which intersection connects only atomic actions.

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LORI Conference 2013 Conference Paper

A Dynamic Deontic Logic Based on Histories

Fengkui Ju
Li Liang

Abstract We aim to present a deontic logic with updates as an extension of Boolean Modal Logic. The features of this logic include the following: (a) deontic relations are defined on sets of finite sequences of states, called histories, and consequently, formulas are evaluated at histories, not states; and (b) it has two dynamic operators, which tend to update the obligation states of agents in different ways. This logic reflects the distinction between the descriptive and prescriptive use of norm sentences.

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LORI Conference 2011 Conference Paper

Update Semantics for Imperatives with Priorities

Fengkui Ju
Fenrong Liu

Abstract Imperatives occur ubiquitously in our social communications. In real life we often get conflicting orders issued by different speakers whose authorities are ranked. We propose a new update semantics to interpret the meaning of imperatives with priorities and illustrate what changes they bring about in the addressee’s cognitive state. The general properties of the semantics, as well as its core philosophical ideas are discussed extensively in this paper.

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