  We prove a shape theorem for a growing set of simple random walks on Z^d,
known as frog model. The dynamics of this process is described as follows:
There are active particles, which perform independent discrete time SRWs, and
sleeping particles, which do not move. When a sleeping particle is hit by an
active particle, the former becomes active as well. Initially, a random number
of particles is placed into each site. At time 0 all particles are sleeping,
except for those placed at the origin. We prove that the set of all sites
visited by active particles, rescaled by the elapsed time, converges to a
compact convex set.
