Exact sequences for equivariantly formal spaces

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.