As we discussed in class, the proof
that there is an pebbling time of $O_d(m/\log m)$
for any dag $G$ with in-degree $\le d$ has a bug
(the construction of $V_a, V_b$ does not work).
Give a fix for this proof so that we can apply it
to for showing $DTIME(t)\ib ATIME(t/\log t)$.

Try to prove as general a result as you can.
More precisely: inn our application, $G$ comes
from creating ``$B$-size blocks'' in the computation
graph.   So one way to fix the proof is to make further
assumptions about the graph $G$.  But we would
prefer to avoid making such restrictions.

<li>
NO: this is actually trivial once you unroll
the computation tree ...


Formalize the proof of Gill (Chapter 8, section 3)
that every recursively enumerable language is accepted
in constant average time.  [We made some intuitively
plausible claims in the text, but these need
to be formalized.]