  In a setting where heterogeneous agents interact to accomplish a given set of
goals, cooperation is of utmost importance, especially when agents cannot
achieve their individual goals by exclusive use of their own efforts. Even when
we consider friendly environments and benevolent agents, cooperation involves
several issues: with whom to cooperate, reciprocation, how to address credit
assignment and complex division of gains, etc. We propose a model where
heterogeneous agents cooperate by forming groups and formation of larger groups
is promoted. Benefit of agents is proportional to the performance and the size
of the group. There is a time pressure to form a group. We investigate how
preferring similar or complement agents in group formation affects an agent's
success. Preferring complement in group formation is found to be better, yet
there is no need to push the strategy to the extreme since the effect of
complementing partners is saturated.
