(This is not a homework question.)
While reading "Digital Computer Electronics" by Albert P. Malvino, I found this circuit on page 121, figure 8-22(a). It claims to be an example of a discrete TTL tri-state buffer, but I believe it to be wrong.
Best I can tell, the output will always be either high or tristated: it will never be low. I also simulated it online, and the results agreed with this assessment. I googled for published errata, but found none.
Would people say this circuit was in error, or am I missing something crucial?