  In answer to Ko's question raised in 1983, we show that an initial value
problem given by a polynomial-time computable, Lipschitz continuous function
can have a polynomial-space complete solution. The key insight is simple: the
Lipschitz condition means that the feedback in the differential equation is
weak. We define a class of polynomial-space computation tableaux with equally
weak feedback, and show that they are still polynomial-space complete. The same
technique also settles Ko's two later questions on Volterra integral equations.
