  In this paper we characterize invertible matrices over an arbitrary
commutative antiring S and find the structure of GL_n (S). We find the number
of nilpotent matrices over an entire commutative finite antiring. We prove that
every nilpotent $n \times n$ matrix over an entire antiring can be written as a
sum of $\lceil \log_2 n \rceil$ square-zero matrices and also find the
necessary number of square-zero summands for an arbitrary trace-zero matrix to
be expressible as their sum.
