Topological rigidity of closures of certain sparse unipotent orbits in finite-volume quotients of ₈=₁ᵏSL₂ (R)

We give a simple proof about the topological rigidity of closures of certain sparse unipotent orbits in G/ where G=₈=₁ᵏSL₂ (R) and is an irreducible lattice in G.