Author’s abstract: “A partial function \(f\) on a \(k\)-element set \(E_{k }\) is a partial Sheffer function if every partial function on \(E_{k }\) is definable in terms of \(f\). Since this holds if and only if \(f\) belongs to no maximal partial clone on \(E_{k }\), a characterization of partial Sheffer functions reduces to finding families of minimal coverings of maximal partial clones on \(E_{k }\). We show that, for each \(k \geq 2\), there exists a unique minimal covering.”