dimensional, time-harmonic waves scattered by periodic domains. For domains assumed to
be at least Lipschitz regular, we propose a novel explicit representation of Sobolev spaces
for quasi-periodic functions that allows for an analysis analogous to that of Helmholtz
scattering by bounded objects. Except for Rayleigh-Wood frequencies, continuity and
coercivity results are derived to prove wellposedness of the associated first kind boundary …