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authorStratis Ioannidis <stratis@stratis-Latitude-E6320.(none)>2012-11-05 13:40:26 -0800
committerStratis Ioannidis <stratis@stratis-Latitude-E6320.(none)>2012-11-05 13:40:26 -0800
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\begin{lemma}\label{lemma:monotone}
-The mechanism is monotone.
+The mechanism is monotone and budget feasible.
\end{lemma}
\begin{proof}
Consider an agent $i$ with cost $c_i$ that is
@@ -25,13 +25,14 @@ The mechanism is monotone.
by the monotonicity and submodularity of $V$. Hence $i\in S_G'$. As $L(\xi)$, is the optimal value of \eqref{relax} under relaxation $L$ when $i^*$ is excluded from $\mathcal{N}$, reducing the costs can only increase this value, so under $c'_i\leq c_i$ the greedy set is still allocated and $s_i(c_i',c_{-i}) =1$.
Suppose now that when $i$ reports $c_i$, $L(\xi) < C V(i^*)$. Then $s_i(c_i,c_{-i})=1$ iff $i = i^*$.
Reporting $c_{i^*}'\leq c_{i^*}$ does not change $V(i^*)$ nor
- $L(\xi) \leq C V(i^*)$; thus $s_{i^*}(c_{i^*}',c_{-i^*})=1$.
-\end{proof}
-\begin{lemma}\label{lemma:budget-feasibility}
-The mechanism is budget feasible.
-\end{lemma}
-\begin{proof}
-Suppose that $L(\xi) < C V(i^*)$. Then the mechanism selects $i^*$. Since the bid of $i^*$ does not affect the above condition, the threshold payment of $i^*$ is $B$ and the mechanism is budget feasible.
+ $L(\xi) \leq C V(i^*)$; thus $s_{i^*}(c_{i^*}',c_{-i^*})=1$, so the mechanism is monotone.
+%\end{proof}
+%\begin{lemma}\label{lemma:budget-feasibility}
+%The mechanism is budget feasible.
+%\end{lemma}
+%\begin{proof}
+
+To show budget feasibility, suppose that $L(\xi) < C V(i^*)$. Then the mechanism selects $i^*$. Since the bid of $i^*$ does not affect the above condition, the threshold payment of $i^*$ is $B$ and the mechanism is budget feasible.
Suppose that $L(\xi) \geq C V(i^*)$.
Denote by $S_G$ the set selected by the greedy algorithm, and for $i\in S_G$, denote by
$S_i$ the subset of the solution set that was selected by the greedy algorithm just prior to the addition of $i$---both sets determined for the present cost vector $c$.