The authors focus their attention on some properties of exponential dichotomy and trichotomy of the linear difference equation
where is a invertible matrix for each . Under the assumptions that this equation has an exponential dichotomy or trichotomy and the invertible matrix is such that is invertible they prove that the perturbed equation
has an exponential dichotomy or trichotomy too, if the norm of is sufficiently small. This result improves some known result on the invariance of exponential dichotomy and trichotomy under some perturbations because the radius of the perturbation considered in the paper is larger than those known. Besides the equivalence between the exponential dichotomy for linear difference equations with almost periodic coefficients in an infinite integer interval and in a finite sufficiently long integer interval is proved. This statement is a discrete version of the corresponding equivalence for an almost periodic differential equation .