This question from introduction to modern cryptography book
Prove this theorem
A private-key encryption scheme II = (Gen, Enc, Dec) has indistinguishabl-e -multiple encryptions in the presence of an eavesdropper if for all probabilistic polynomial-time adversaries A there exists a negligible function neg I such that
- Pr [PrivK A,II (n) = 1 ] J <= 1/2 + negl(n),
where the probability is taken over the random coins used by A, as well as the random coins used in the experiment (for choosing the key and the random · bit b, as well as for the encryption itself)