Abstract

Let T and T1 be tournaments with n elements, E a basis for T, E′ a basis for T′, and k ≥ 3 an integer. The dual of T is the tournament T” of basis E defined by T = T for all x, y ε E. A hemimorphism from T onto T′ is an isomorphism from T onto T” or onto T. A k-hemimorphism from T onto T′ is a bijection f from E to E′ such that for any subset X of E of order k the restrictions T/X and T1/f are hemimorphic. The set of hemimorphisms of T onto itself has group structure, this group is called the group of hemimorphisms of T. In this work, we study the restrictions to n – 2 elements of a tournament with n elements. In particular, we prove: Let k ≥ 3 be an integer, T a tournament with n elements, where n ≥ k + 5. Then the following statements are equivalent: All restrictions of T to subsets with n – 2 elements are k-hemimorphic. All restrictions of T to subsets with n – 2 elements are 3-hemimorphic. All restrictions of T to subsets with n – 2 elements are hemimorphic. All restrictions of T to subsets with n – 2 elements are isomorphic, Either T is a strict total order, or the group of hemimorphisms of T is 2-homogeneous