In this post, Ofer says that taking the convex combination of two Girsanov measures yields a drift $BF_1+(1-B)F_2$ where $B$ is a Bernoulli random variable with parameter $\lambda$, independent of the underlying probability measure. I am a bit confused - where does the mixing occur? Why do we have to enlarge the space?
Since $\mu=\lambda\mu_1+(1-\lambda)\mu_2$ is a Girsanov measure there is a drift in the original space, you shouldn't have to enlarge it, right?