The output is the inverted carry of carry inputs
<SPAN CLASS="boldred">a</SPAN> and <SPAN CLASS="boldred">c</SPAN>
and the carry of input <SPAN CLASS="boldred">b</SPAN>.
The stage efforts for pin <SPAN CLASS="boldred">b</SPAN>
is 1.6, 1.9 and 2.4 for the x05,
x1 and x2 drive strengths respectively.
The cells here use a P/N ratio of about 2.