  Concurrent games with a fixed number of agents have been thoroughly studied,
with various solution concepts and objectives for the agents. In this paper, we
consider concurrent games with an arbitrary number of agents, and study the
problem of synthesizing a coalition strategy to achieve a global safety
objective. The problem is non-trivial since the agents do not know a priori how
many they are when they start the game. We prove that the existence of a safe
arbitrary-large coalition strategy for safety objectives is a PSPACE-hard
problem that can be decided in exponential space.
