[Solved] Dynamical Homework 7

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1.1 Section 3.7 Problem 2.

Observe that the only T-invariant subset of X is X itself. Suppose we have a subset A of X such that A 6= X. Then there exists aj X such that a(j+1) mod n 6 A and hence, T(aj) 6 A. Thus A is not T-invariant. Hence, we must have A = X. But AC = XC = . So (AC) = 0 whenever A is T-invariant, and so T is ergodic.

Problem 3.

Suppose T is a totally ergodic measure-preserving transformation and suppose that T is invertible. Since T is ergodic, observe that (A) = 0 or (AC) = 0 for any T-invariant set A. Now fix a T-invariant set A and suppose (A) = 0. Since T is measure-preserving, we have that if (A) = 0, then (T1(A)) = 0.

For T2(A), observe that we have

T2(A) = T1(T1(A)) = T1(B)

where B = T1(A), a measure 0 set. Again, since T is measure-preserving and (B) = 0, we have that (T1(B)) = (T2(A)) = 0. Proceeding inductively, we get that if (A) = 0, then (Tn(A)) = 0 for all n < 0. Moreover, if A is T-invariant, then A is also T1-invariant, since T is invertible. This again applies for Tn with any n < 0, so we have that Problem 6.

Recall the the two dimensional Bakers transformation is defined as

y

(2x, ), if 0 x < 1/2

T(x,y) = 2

, if 1/2 x 1

For any subset A of [0,1] [0,1], we have that (A) =

1

1.2 Section 3.10 Problem 1.

Problem 3.

Problem 4.

Problem 6.

2

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[Solved] Dynamical Homework 7
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