© 2000 by London Mathematical Society
© The London Mathematical Society
Essential Equivariant Maps and BorsukUlam Theorems
aw Marzantowicz
Instituto de Matemáticas, Universidad Nacional Autónoma de México 04510 México DF, Mexico, mclapp{at}math.unam.mx
Faculty of Mathematics and Computer Science, A Mickiewicz University Pozna
, Poland, marzan{at}math.amu.edu.pl
Received 8 October 1998. Revision received 18 January 1999.
A full characterization is given of those compact Lie groups G with the property that every G-map X
X on a finite-dimensional G-complex X of finite orbit type, XG = Ø, is (non-equivariantly) essential. For arbitrary G, conditions are given on the G-space X which guarantee this property. Finally, conditions are given for the non-existence of a G-map X
Y inducing a homotopy equivalence XG
YG on the fixed point sets. These results have applications to critical point theory of almost G-invariant functionals.