Post algebra

An algebra $(P,\Omega)$, where $P$ is a set of functions and $\Omega$ is a set of operations equivalent to composition operations with different types of restrictions. Finite-valued and countable-valued logics, logics of non-homogeneous functions, etc., are examples of Post algebras. In fact, the problems encountered in the theory of Post algebras essentially coincide with the problems in the theory of many-valued logic.

For references see Many-valued logic.