It is well-known that every monounary variety of total algebras has one-element equational basis (see [5]). In my paper I prove that every monounary weak variety has at most 3-element equational basis. I give an example of monounary weak variety having 3-element equational basis, which has no 2-element equational basis.
It is known that (ℤₙ,-ₙ) are examples of entropic quasigroups which are not groups. In this paper we describe the table of characters for quasigroups (ℤₙ,-ₙ).
In this paper we show that there exists an infinite family of pairwise non-isomorphic entropic quasigroups with quasi-identity which are directly indecomposable and they are two-generated.
In this paper we present representation of finite effect algebras by matrices. For each non-trivial finite effect algebra we construct set of matrices in such a way that effect algebras and are isomorphic if and only if . The paper also contains the full list of matrices representing all nontrivial finite effect algebras of cardinality at most .
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