Spectral analysis for finite rank perturbation of diagonal operator in non-archimedean Banach space of countable type

In this paper we are concerned with the spectral analysis for classes of finte rank perturbations diagonal operators in form A = D+F where D is a operator and F u’1 ⊗v’1+...+u’m ⊗vm an finite non-archimedean Banach space countable type. We compute spectrum using theory Fredholm non archimedean setting concept essential linear operators.