diff --git a/fzd/fzd.tex b/fzd/fzd.tex
index 6196d4a..695b720 100644
--- a/fzd/fzd.tex
+++ b/fzd/fzd.tex
@@ -374,10 +374,13 @@ i.e. for a Venn N diagram  $Z\# = N^{2}$
 \endequation
 
 
- But for any diagram less
+But for any diagram less
 complicated than Venn N, where $ Z\# $ 
 is small in comparison with $2^{N}$ the algorithm becomes far more efficient.
-
+For FMMD failure analysis Venn 2 combinations are rare
+and Venn 3 or 4 would only be required for special cases
+(such as common components with a serial safety dependency; 747 engines;
+relays contacts in series etc)
 Examples of complexity savings are shown in section \ref{complexity}.
 
 
@@ -477,17 +480,29 @@ contour against all others a collection of pure intersection relationships
 and enclosure relationships can be determined.
 This forms a list of relationship pairs from the cross product of all the contours.
 
+%\equation
+%%\label{crossprodsingle}
+%\begin{array}{l}
+% pi(a,b) \; \Rightarrow
+%%\stackrel{\Delta}{=} 
+%  \; \forall    \;  C \; \bullet \; a   \;  X  \;   \forall C \; \bullet \; b  \\
+% \;  \bullet   (a \cap b)  \; \wedge \; \neg (a \supseteq b) \; \wedge \; \neg  (b \supseteq a) \\
+%\end{array}
+%\endequation
+%
+
+
 \equation
 %\label{crossprodsingle}
 \begin{array}{l}
- pi(a,b) \; \Rightarrow
-%\stackrel{\Delta}{=} 
-  \; \forall    \;  C \; \bullet \; a   \;  X  \;   \forall C \; \bullet \; b  \\
- \;  \bullet   (a \cap b)  \; \wedge \; \neg (a \supseteq b) \; \wedge \; \neg  (b \supseteq a) \\
+ pi(a,b) \; \implies
+ a \in D \wedge b \in D \wedge a \neq b \wedge  
+ \; (a \cap b)  \; \wedge \; \neg (a \supseteq b) \; \wedge \; \neg  (b \supseteq a) \\
 \end{array}
 \endequation
 
-
+Or in other words, a pure intersection is where the contours $a$ and $b$ in the diagram $D$
+where $a$ intersects $b$ but $a$ does not enclode $b$ and $b$ does not enclose $a$.
 \begin{figure}[h]
  \centering
  \includegraphics[width=200pt,bb=0 0 452 290,keepaspectratio=true]{fzd/pice.jpg}
@@ -517,13 +532,23 @@ This again, forms a list of relationship pairs from  cross product of all the co
 \equation
 %\label{crossprodsingle}
 \begin{array}{l}
- enc(a,b) \; 
-%\stackrel{\Delta}{=}
-\Rightarrow \; \forall   \;  C \; \; \bullet a   \;  X  \;   \forall  \;  C   \; \bullet \; b  \\
- \;  \bullet   (a \supset b)   \\
+ enc(a,b) \;  \implies
+ a \in D \wedge b \in D \wedge a \neq b \wedge  
+ (a \supset b) 
 \end{array}
 \endequation
 
+%
+%\equation
+%%\label{crossprodsingle}
+%\begin{array}{l}
+% enc(a,b) \; 
+%%\stackrel{\Delta}{=}
+%\Rightarrow \; \forall   \;  C \; \; \bullet a   \;  X  \;   \forall  \;  C   \; \bullet \; b  \\
+% \;  \bullet   (a \supset b)   \\
+%\end{array}
+%\endequation
+%
 
 \section{The Pure Intersection Chain}