<t>In the HJM model, the short rate is given byr_u = f(0,u) + Integral[0,u]alpha(s,u)ds + Integral[0,u]sigma(s,u)dW_sr_u is then integrated and Fubini is applied to produce:Integral[0,t]r_u du = Integral[0,t]f(0,u)du - Integral[0,t]Integral[s,t]alpha(s,u)duds + Integral[0,t]Integral[s,t]sigma(s,u)du...