A non-dualisable entropic algebra.
An algebra \(\mathcal A = \langle A,F\rangle \) is called entropic if every operation \(f \in F\) is a homomorphism \(f\) : \(A^{n} \rightarrow A\), where \(n\) is the arity of \(f\). Some of the first known examples of dualisable algebras were entropic. The authors give an example of a five-element unary algebra which is entropic but does not admit a natural duality.
scientific article; zbMATH DE number 2158764