Even though in Artificial Intelligence, a set of logical formulas is often called a belief base, reasoning about beliefs requires more than the language of classical logic. This paper proposes a simple logic whose atoms are beliefs and formulas are conjunctions, disjunctions and negations of beliefs. It enables an agent to reason about some beliefs of another agent as revealed by the latter. This logic, called MEL, borrows its axioms from the modal logic KD, but it is an encapsulation of propositional logic rather than an extension thereof. MEL bears some closer formal connection with Pauly's consensus logic. Its semantics is in terms of subsets of interpretations, and the models of a formula in MEL is a family of subsets of interpretation. It captures the idea that if the epistemic state of an agent about the world is represented by a subset of possible worlds, the meta-epistemic state of another agent about the former's epistemic state is a family of such subsets. We prove that any family of subsets of interpretations can be expressed as a single formula in MEL. This formula is a symbolic counterpart of the Moebius transform in the theory of belief functions.