at.algebraic topology - Burnside ring and zeroth G-equivariant stem for finite G

This is from Segal's paper

Equivariant stable homotopy theory. Actes du Congrès International des Mathématiciens (Nice, 1970), Tome 2, pp. 59--63. Gauthier-Villars, Paris, 1971.

MR0423340 (54 #11319)

where he states that the equivariant stable cohomotopy of $S$ is $pi_G^{-ast}(S)=bigoplus_Kpi_{ast}^s(B(N_G(K)/K)^+)$. In particular, $pi_G^0(S)$ is the Burnside ring.