Paper 3 , Section II, J

Probability and Measure
Part II, 2015

(a) Let (E,E,μ)(E, \mathcal{E}, \mu) be a measure space. What does it mean to say that T:EET: E \rightarrow E is a measure-preserving transformation? What does it mean to say that a set AEA \in \mathcal{E} is invariant under TT ? Show that the class of invariant sets forms a σ\sigma-algebra.

(b) Take EE to be [0,1)[0,1) with Lebesgue measure on its Borel σ\sigma-algebra. Show that the baker's map T:[0,1)[0,1)T:[0,1) \rightarrow[0,1) defined by

T(x)=2x2xT(x)=2 x-\lfloor 2 x\rfloor

is measure-preserving.

(c) Describe in detail the construction of the canonical model for sequences of independent random variables having a given distribution mm.

Define the Bernoulli shift map and prove it is a measure-preserving ergodic transformation.

[You may use without proof other results concerning sequences of independent random variables proved in the course, provided you state these clearly.]