Crucial to this program is "Zimmer's cocycle superrigidity theorem", a generalization of Grigory Margulis's superrigidity theorem. Like Margulis's work, which greatly influenced Zimmer, it uses ergodic theory as a central technique in the case of invariant measures. It led to many results within the Zimmer Program, although many of the main conjectures remain open. In addition to Margulis, Zimmer was greatly influenced by the work of Mikhail Gromov on rigid transformation groups and he extended and connected Gromov's theory to the Zimmer Program.