Choice functions on posets

In the paper we study choice functions on posets satisfying the conditions of heredity and outcast. For every well-ordered sequence of elements of poset, we define the corresponding `elementary’ choice function. Every such a choice function satisfies the conditions of heredity and outcast. Inversely, every choice functions satisfying the conditions of heredity and outcast can be represented as union of several elementary choice functions. This result generalizes the Aizerman-Malishevsky theorem about structure of path-independent choice functions.