double simultaneous auto check possibility

logic_diagram/logic_diagram.tex

@@ -812,6 +812,9 @@ Note that we have here all the single and double failure test cases in one diagr
  \label{fig:doublesim}
 \end{figure}
 
+\paragraph{Automated checking of double failure mode conditions}
+A PLD editor can be set to ensure that each diagram has a test case for every 
+double simultaneous failure instance.
 
 \section{N Simultaneous Errors}
 
@@ -834,10 +837,6 @@ possibility into the design.
  \label{fig:allfour}
 \end{figure}
 
-
-TO DO:
-Venn N example
-
 %\subsection{Example Sub-system}
 %
 %For instance were a `power supply' being analysed there could be several