Yoda lies to R2-D2 to keep the secret

Yoda pretends not to know R2-D2 during their reunion on Dagobah in The Empire Strikes Back, thus resolving an apparent contradiction with the prequel trilogy. This staging is confirmed in the novel From a Certain Point of View, written for the forty years of the saga. This subterfuge allows the Jedi master to preserve his cover in front of Luke Skywalker.