Lectures on the Topology of 3-Manifolds_ An Introduction To The Casson Invariant 2nd Edition by Nikolai Saveliev

Progress in low-dimensional topology has been very quick in the last three decades, leading to the solutions of many difficult problems. Among the earlier highlights of this period was Casson’s λ-invariant that was instrumental in proving the vanishing of the Rohlin invariant of homotopy 3-spheres.