\documentclass{article}
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\begin{document}



\begin{align*}
&C(v_1) + C(v_2) + C(v_5) + C(v_6)
\\&\geq C(v_1) + C(v_2) + C(v_5) + C(v_6) - 2*c(v_1, v_2)
\\&= C(v_1,v_2) + C(v_5) + C(v_6)
\\&\geq C(v_1,v_2) + C(v_5) + C(v_6) - 2*c(v_1 v_2, v_6)
\\&= C(v_1,v_2, v_6) + C(v_5)
\\&\geq C(v_1,v_2, v_3) + C(v_5)
\\&\geq  C(v_1,v_2, v_3) + C(v_5) - 2*c(v_1 v_2 v_3, v_5)
\\&=  C(v_1,v_2, v_3, v_5)
\\&\geq  C(v_1,v_2, v_3, v_4)
\end{align*}

\end{document}