diff --git a/notes.tex b/notes.tex index f4133f6..9204938 100644 --- a/notes.tex +++ b/notes.tex @@ -160,14 +160,14 @@ Now we prove \autoref{contraction_gap}. \begin{proof} We follow the same framework as the graphic case. Let $c$ be the 2-hitting set gap and let $c'$ be the cogirth-packing gap of $M$. We have \begin{equation}\label{eq1} -\lambda(M'/t)\leq \lambda_2(G)\leq c\sigma_2(G)\leq c(|J|+\sigma(M'/T)|_{E\setminus J}) +\lambda(M'/\tau)\leq \lambda_2(M)\leq c\sigma_2(M)\leq c(|J|+\sigma(M'/T)|_{E\setminus J}) \end{equation} -where $J$ is the minimum hitting set of $\{C(B,f)\setminus f|\forall B\}$. +where $J$ is the minimum hitting set of $\{C(B,f)\setminus f|\forall B\}$ and $\lambda_2(M)$ ($\sigma_2(M)$) is the integral (fractional) 2-hitting set of bases of $M$. We then apply \autoref{TcutTjoin}. -If $\lambda(M'/t)=\lambda(M)$, then we have $\lambda(M'/t)= \lambda(M)\leq c \sigma(M)\leq c\sigma(M'/t)$, since the optimal solution to $\sigma(M'/t)$ is feasible to $\sigma(M)$; -Otherwise, we extend \autoref{eq1} and get $\lambda(M'/t)\leq c(|J|+\sigma(M'/T))=c(\lambda(M)+\sigma(M'/T))\leq c(c'+1)\sigma(M'/T)$. +If $\lambda(M'/\tau)=\lambda(M)$, then we have $\lambda(M'/\tau)= \lambda(M)\leq c \sigma(M)\leq c\sigma(M'/\tau)$, since the optimal solution to $\sigma(M'/\tau)$ is feasible to $\sigma(M)$; +Otherwise, we extend \autoref{eq1} and get $\lambda(M'/\tau)\leq c(|J|+\sigma(M'/\tau))=c(\lambda(M)+\sigma(M'/\tau))\leq c(c'+1)\sigma(M'/\tau)$. \end{proof} To finish the proof of constant gap of $M/T$ we note that $(M/T_t)|E(G)=M/T$ and $(M/T_{i+1})|E(G)=[((M/T_{i})|E(G))+e_{i+1}]/e_{i+1}$ and the constant gap for deletion minors can be proven by wrapping the entire proof into an induction on the size of $E(G)$.