2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/115424These notes contain an Ergodic-theoretic account of the Cocycle Superrigidity Theorem recently discovered by Sorin Popa. We state and prove a relative version of the result, discuss some applications to measurable equivalence relations, and point out that Gaussian actions (of ``rigid'' groups) satisfy the assumptions of Popa's theorem.v.2: slight changes in the presentation, (some) typos corrected, wq-normal subgroups added. 35 pagesDynamical SystemsOperator Algebras37A20text