Telescopic cascode op amp with input and output shorted
This condition does not look right to me.

Since Vout ~ Vin we can write
$$
V_x = V_{in} - V_{gs2} + V_{dsat2} = V_{in} - V_{th2}
$$
and further
$$
V_b &gt; V_x + V_{gs4} = V_{in} - V_{th2} + V_{gs4}
$$
with \$V_{th2} \approx V_{th4}\$
this results in the following condition
$$
V_b &gt; V_{in} + V_{dsat4}
$$
which looks reasonable.