The output is the inverted carry of carry input
<SPAN CLASS="boldred">c</SPAN> and the inverse of inputs
<SPAN CLASS="boldred">a</SPAN> and <SPAN CLASS="boldred">b</SPAN>.
The stage efforts are 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.