  ![ $$\\displaystyle{X_{0}\\mapsto \\left \\{\\begin{array}{ll} 0, &\\mbox{ $\\tau < T_{0}$} \\\\ \\lambda _{0} \\cdot e^{-\\lambda _{0}\(\\tau -T_{0}\)},&\\mbox{ $\\tau \\geq T_{0}$} \\end{array} \\right.}$$ ](A000000_0_En_0_Chapter_Equ