<p>Recently, many combinatorial notions have been found to have infinite partition and almost disjoint properties, which state that in a given semigroup of cardinality <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\kappa \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>κ</mi> </math></EquationSource> </InlineEquation>, these notions can be partitioned into <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\kappa \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>κ</mi> </math></EquationSource> </InlineEquation> subsets with the same property; moreover, if <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\kappa \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>κ</mi> </math></EquationSource> </InlineEquation> contains <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\delta \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>δ</mi> </math></EquationSource> </InlineEquation> almost disjoint subsets, then the notion contains <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\delta \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>δ</mi> </math></EquationSource> </InlineEquation> almost disjoint subsets of that type. In this paper, we investigate two notions: <i>C</i>-sets and <i>J</i>-sets in non-commutative semigroups. We obtain that in some non-commutative structures, such as free semigroups, free groups, general linear groups, and the Heisenberg group, <i>C</i>-sets and <i>J</i>-sets still have infinite partition and almost disjoint properties.</p>

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Infinite partition and almost disjoint properties of C-sets and J-sets in non-commutative semigroups

  • Teng Zhang

摘要

Recently, many combinatorial notions have been found to have infinite partition and almost disjoint properties, which state that in a given semigroup of cardinality \(\kappa \) κ , these notions can be partitioned into \(\kappa \) κ subsets with the same property; moreover, if \(\kappa \) κ contains \(\delta \) δ almost disjoint subsets, then the notion contains \(\delta \) δ almost disjoint subsets of that type. In this paper, we investigate two notions: C-sets and J-sets in non-commutative semigroups. We obtain that in some non-commutative structures, such as free semigroups, free groups, general linear groups, and the Heisenberg group, C-sets and J-sets still have infinite partition and almost disjoint properties.