add forgotten space

src/flow.tex

@@ -310,7 +310,7 @@ temperature \(β\).
 There are multiple ways of approaching finite
 temperature~\cite{Diosi1997,Diosi1998Mar}. One is to \emph{purify} the
 bath initial state by introducing additional degrees of
-freedom\footnote{Also called the \emph{thermofield}
+freedom~\footnote{Also called the \emph{thermofield}
   method~\cite{Takahashi1996Jun,Semenoff1983Jun}.}. This has the
 advantage of yielding a particularly simple result in the case of
 self-adjoint coupling \(L=L^\dag\). In that case, one may simply