\[\operatorname{nc}(u+v)=\frac{\operatorname{nc}u\operatorname{nc}v+%
\operatorname{sc}u\operatorname{dc}u\operatorname{sc}v\operatorname{dc}v}{1-{k%
^{\prime}}^{2}{\operatorname{sc}}^{2}u{\operatorname{sc}}^{2}v},\]