%exm0634_3.m
syms tao;
t=sym('t','positive');												%<4>
ut=sym('Heaviside(t)-Heaviside(t-1)');
ht=t*exp(-t);
yt53=int(subs(ut,t,tao)*subs(ht,t,t-tao),tao,0,t);
yt53=collect(yt53,'Heaviside(t-1)')