some questions for Forensics

Last week，I'm looking for indexing infornation for Forensics. Is not understood very much regarding some questions：

Questions 1:
| Pr [ x(i1) x(i2)...x(ik) = a ] - 2(-k)|<(or=) e

2(-k) - e <(=) Pr[x(i1) x(i2)...x(ik) = a ] <(=) 2(-k) +e

Questions 2:
t = 6(d+1) (d+2) [In n]

at = fk[x1 || x2 ||...||x(m)]