In this paper, we discuss almost periodicity of solutions for evolution equations in Banach space. We introduce the concept of difference-variation equation. For a special Hilbert space, we establish some results on almost periodicity of all solutions for evolution equations. In particular, we extend Haraux's result on $R^2$ to $R^n.$
"Almost periodicity of solutions for almost periodic evolution equations." Differential Integral Equations 18 (4) 469 - 480, 2005.