Epistemic logic

• □ φ: ‘we know that φ is true’ (also written Kφ)
• ◇ φ: ‘we consider φ possible’
• [i] φ: ‘agent i knows that φ is true’ (also written Kᵢφ)
• 〈i〉φ: ‘agent i considers φ possible’

In an epistemic frame, the relation statement sRᵢt means: given his information in situation s, agent i considers t possible