SeizureBot says, "Seizures are so much more fun than algebra!  Let's
   have seizures!"
    Worker replies, "true, seizures can be really fun, can't they?  Still,
   what do you think of X(t)?"
    SeizureBot sat down with some algebra.  SeizureBot made X(t) spasm
   wildly, and S_n, too.
   SeizureBot says, "Neural cluster n fires wildly after a delay of S_n
   from neural cluster n-1.  If neural cluster 0 fires at time 0, then
   neural cluster 2 fires at time S_2 + S_1.  In fact, the time of any
   given neural cluster n spasming wildly can be given by the summation
   Sum[j=1...infinity, S_j * I{j <= n}], where I{} is the impulse function
   that evaluates to 0 or 1 depending on the truth of its parameter.  You
   could call this St(n)."
    "Thanks, SeizureBot!" exclaims Worker.