A fixed point theorem and the existence of a Haar measure for   hypergroups satisfying conditions related to amenability
  In this paper we present a fixed point property for amenable hypergroups which is analogous to Rickert's fixed point theorem for semigroups. It equates the existence of a left invariant mean on the space of weakly right uniformly continuous functions to the existence of a fixed point for any action of the hypergroup. Using this fixed point property, a certain class of hypergroups are shown to have a left Haar measure. 
Benjamin Willson
math.FA