<t>A mistake seems to be here.First, in Ito's formula for H(t,W(t))=F(t)W(t) with dF/dt=f we have (H(t,x) = F(t)x; H_t(t,x) = f(t)x, H_x(t,x) = F(t), H_xx(t,x) = 0)dF(t)W(t) = f(t)W(t)dt + F(t)dW(t) (last term is correct now),which yieldsint {f(s)W(s)ds} = F(t)W(t) - int {F(s)dW(s)}.We have X = F(t)...