Equivariant maps of joins of finite G-sets and an application to critical point theory
A lower estimate is proved for the number of critical orbits and critical values of a G-invariant C¹ function , where G is a finite nontrivial group acting freely and orthogonally on . Neither Morse theory nor the minimax method is applied. The proofs are based on a general version of Borsuk’s Antipodal Theorem for equivariant maps of joins of G-sets.