  Let T be a torus. We present an exact sequence relating the relative
equivariant cohomologies of the skeletons of an equivariantly formal T-space.
This sequence, which goes back to Atiyah and Bredon, generalizes the so-called
Chang-Skjelbred lemma. As coefficients, we allow prime fields and subrings of
the rationals, including the integers. We extend to the same coefficients a
generalization of this "Atiyah-Bredon sequence" for actions without fixed
points which has recently been obtained by Goertsches and Toeben.
