Hi !
I cannot get rid of HoldForm from my expression despite ReleaseHold invokation.
Here is the code :
 x3 = (1/(2*r*((-tau)*tau1 + Q*(tau^2 + tau1^2))))*(a*Q*tau1*
     HeavisideTheta[
      t - t1]*(-2*p0*r*
        tau1 + (-2*Q*Sqrt[r]*tau + tau1 - 4*Q^2*tau1 + Sqrt[r]*tau1)*
        HoldForm[
         HoldForm[
           E^((Sqrt[r]*t)/(2*Q*tau))*
            HoldForm[
             E^(t1/(2*Q*tau))*
             HoldForm[1/(E^((Sqrt[r]*t1)/(2*Q*tau))*E^(t1/tau1))]]]/
         E^(t/(2*Q*tau))] + (2*Q*Sqrt[r]*tau + 
         tau1 - (4*Q^2 + Sqrt[r])*tau1)*
       HoldForm[
        HoldForm[
          HoldForm[
            E^(t1/(2*Q*tau))*
             HoldForm[E^((Sqrt[r]*t1)/(2*Q*tau))/E^(t1/tau1)]]/
           E^((Sqrt[r]*t)/(2*Q*tau))]/E^(t/(2*Q*tau))]))
FullForm[x3]
x3 = ReleaseHold[x3]
FullForm[x3]
May I ask you some hints ?
Regards