The concept of genus of an
invariant, closed set A in a paracompact free G-space E is introduced for any
compact Lie group G and the general result that G-genus A =catBA∗ is proven
where B = E∕G, A∗= E∕G and cat is short for Ljusternick-Schnirelman category.
As a special case, the concept of genus (Krasnoselskii) coincides with the notion of
category (Ljusternik-Schnirelman) as employed in a real or complex Banach
space.