14.6 For a simple random walk Sn, which of the following are stopping times?

a) T1 = min{n ≥ 3 | Sn = Sn−3 + 3},

b) T2 = min{n ≥ 3 | Sn = Sn−3 + 2},

c) T3 = T1 + 3,

d) T4 = T2 ∧ T3,

e) T5 = T1 ∨ 5.