  Toeplitz matrices have applications to different problems of statistical
mechanics. Recently they were used for calculation of entanglement entropy in
spin chains. We use the Fisher-Hartwig formula to calculate entanglement
entropy of large block of spins in the ground state of XY spin chain. We also
calculate Renyi entropy and prove that the spectrum of the density matrix of a
block of spins is exact geometric sequence [also different eigenvalues are
degenerated differently].
