“…In conclusion, we mention some papers that considered the norm-resolvent convergence for operators with periodic rapidly oscillating coefficients: in [10,30,35,47,56,58] the authors established sharp estimates for the rates of convergence in the sense of various operator norms. Norm-resolvent convergence was established also for certain perturbations in the boundary homogenisation: in [11,12], where problems with frequent alternation (periodic and non-periodic) of boundary conditions were treated, in [15], [46,Ch.…”