讲座内容：

Let G be S_N, the finitary permutation (i.e., permutations with finite support) group on the set of positive integers N. We prove that G has the invariant von Neumann subalgebras rigidity (ISR, for short) property as introduced in Amrutam–Jiang's work. More precisely, every Ginvariant von Neumann subalgebra P ⊆ L(G) is of the form L(H) for some normal subgroup H of G and in this case, H = {e}, A_N or G, where A_N denotes the finitary alternating group on N, i.e., the subgroup of all even permutations in S_N. This gives the first known example of an infinite amenable group with the ISR property.