Consider a game where a referee chooses (x,y) according to a publicly known
distribution; sends x to Alice, and y to Bob. Without communicating
with each other, Alice responds with a value a and Bob responds with a
value b. Alice and Bob jointly win if a publicly known predicate
Q(x,y,a,b) is satisfied.

Assume that the maximum probability that Alice and Bob can win in
such a game is v < 1. Raz (SIAM J. Comput. 27, 1998) shows that if
the game is repeated n times in parallel, then the probability
that Alice and Bob win all games simultaneously is at most
(v')^{n/log(s)) where s is the maximal number of possible responses
from Alice and Bob in the initial game, and v' is a constant depending
only on v.

In this work, we simplify Raz's proof in various ways and thus
shorten it significantly. Further we study the case where Alice and
Bob are not restricted to local computations and can use any
strategy which does not imply communication between them.