Exercise 13.4. Prove that in the model of Section 13.1, if V (, t0 )=1 and there

Exercise 13.4. Prove that in the model of Section 13.1, if ηV (ν, t0 )=1 and there is entry at some t0 , then ηV (ν, t)=1 for all t and conversely that if ηV (ν, t0 ) < 1 for some t 0 , then ηV (ν, t) ≤ 1 for all t and there is no entry at any t.