In the logic-based approach, a syntax and semantics have been built using the language of modal logic, which we will now describe. The basic modal operator of epistemic logic, usually written "K", can be read as "it is known that," "it is epistemically necessary that," or "it is inconsistent with what is known that not." If there is more than one agent whose knowledge is to be represented, subscripts can be attached to the operator (formula_1, formula_2, etc.) to indicate which agent one is talking about. So formula_3 can be read as "Agent formula_4 knows that formula_5." Thus, epistemic logic can be an example of multimodal logic applied for knowledge representation.