Let $B(t,T)$ denote the cost at time t of a risk-free 1 euro bond, at time T. Assume that the interest rate is a deterministic function. Show that the absence of arbitrage requires that:
$ B(0,1) B(1,2) = B(0,2)$
For instance, could you give a detailed explanation of what to do if $B(0,1)B(1,2) > B(0,2)$ ?