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There are continuum many clones on a three-element set even if they are considered up to emph{homomorphic equivalence}. The clones we use to prove this fact are clones consisting of emph{self-dual operations}, i.e., operations that preserve the relation ${(0,1),(1,2),(2,0)}$. However, there are only countably many such clones when considered up to equivalence with respect to emph{minor-preserving maps} instead of clone homomorphisms. We give a full description of the set of clones of self-dual operations, ordered by the existence of minor-preserving maps. Our result can also be phrased as a statement about structures on a three-element set, ordered by primitive positive constructability, because there is a minor-preserving map from the polymorphism clone of a finite structure $mathfrak A$ to the polymorphism clone of a finite structure $mathfrak B$ if and only if there is a primitive positive construction of $mathfrak B$ in $mathfrak A$.
The kernel relation $K$ on the lattice $mathcal{L}(mathcal{CR})$ of varieties of completely regular semigroups has been a central component in many investigations into the structure of $mathcal{L}(mathcal{CR})$. However, apart from the $K$-class of t
The study of partial clones on $mathbf{2}:={0,1}$ was initiated by R. V. Freivald. In his fundamental paper published in 1966, Freivald showed, among other things, that the set of all monotone partial functions and the set of all self-dual partial fu
For a class C of operations on a nonempty base set A, an operation f is called a C-subfunction of an operation g, if f = g(h_1, ..., h_n), where all the inner functions h_i are members of C. Two operations are C-equivalent if they are C-subfunctions
Let A be a finite non-singleton set. For |A|=2 we show that the partial clone consisting of all selfdual monotone partial functions on A is not finitely generated, while it is the intersection of two finitely generated maximal partial clones on A. Mo
In this paper, we construct self-dual codes from a construction that involves 2x2 block circulant matrices, group rings and a reverse circulant matrix. We provide conditions whereby this construction can yield self-dual codes. We construct self-dual