Fixed typo.

app_notation-background.tex

@@ -56,7 +56,8 @@ Importantly, as the following proposition shows, any finite $\semN$-PDB can be e
 \begin{proof}
 To prove that \abbrNXPDB\xplural are complete consider the following construction that for any $\semN$-PDB $\pdb = (\idb, \pd)$ produces an \abbrNXPDB $\pxdb = (\db_{\semNX}, \pd')$  such that $\rmod(\pxdb) = \pdb$. Let $\idb = \{D_1, \ldots, D_{\abs{\idb}}\}.$ %and let $max(D_i)$
 \AH{What are we using $max(D_i)$ for?}
- denote $max_{\tup} D_i(\tup)$. For each world $D_i$ we create a corresponding variable $X_i$.
+ %denote $max_{\tup} D_i(\tup)$. 
+ For each world $D_i$ we create a corresponding variable $X_i$.
 %variables $X_{i1}$, \ldots, $X_{im}$ where $m = max(D_i)$.
 In $\db_{\semNX}$ we assign each tuple $\tup$ the polynomial:
 %