  We compute electromagnetic, gravitational and mixed linear response functions
of two- dimensional free fermions in external quantizing magnetic field at an
integer filling factor. The results are presented in the form of the effective
action and as an expansion of currents and stresses in wave-vectors and
frequencies of the probing electromagnetic and metric fields. We identify the
terms in linear response functions coming from geometric Chern-Simons, Wen-Zee,
and gravitational Chern-Simons terms in effective action. We derive the
expressions for Hall conductivity, Hall viscosity and find the current and
charge density responses to the spatial curvature as well as stresses caused by
inhomogeneous electromagnetic fields.
