I have a serious point to make with that, and that is that the assumption that there is a single lowest interest rate at which it is possible to both lend and borrow is simply not true. Well, it might be true for banks (i.e., market makers), for instance in London they can all borrow from each other at LIBOR, but other market participants don't have access to that, and can borrow and lend at different rates.

Those whom the Gods wish to destroy They first make mad. -- Euripides