Update wording

Paper.tex

@@ -247,7 +247,7 @@ \subsection{World State} \label{ch:state}
 \quad\equiv\quad \boldsymbol{\sigma}[a] = \varnothing \vee \mathtt{\tiny EMPTY}(\boldsymbol{\sigma}, a)
 \end{equation}
 
-Here is a function that updates the balance of an account state but deletes the account state when it becomes empty:
+We define a function that updates the balance of an account state but deletes the account state when it becomes empty:
 \begin{equation}
 \rho_b(\boldsymbol{\sigma}, a, x) \equiv
 \begin{cases}