diff --git a/logic_diagram/examplepld.dia b/logic_diagram/examplepld.dia
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diff --git a/logic_diagram/examplepld.jpg b/logic_diagram/examplepld.jpg
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diff --git a/logic_diagram/logic_diagram.tex b/logic_diagram/logic_diagram.tex
index 43249c4..9d236f2 100644
--- a/logic_diagram/logic_diagram.tex
+++ b/logic_diagram/logic_diagram.tex
@@ -128,7 +128,7 @@ All features may be labelled, and the labels must be unique within a diagram, ho
 %Regions defined by contours are used to represent given conjunctive logical conditions.
 
 Test~cases are marked by asterisks. The asterisk is used rather than a point, because is analogous to the constraint
-diagram universal qualifier~\cite{uconstraintd}. These are used as a visual `anchor'
+diagram universal qualifier~\cite{howse:spider}. These are used as a visual `anchor'
 to mark a logical condition, the logical condition being defined by the contours
 that enclose the region on which the test~case has been placed.
 The contours that enclose represent conjunction.
@@ -169,7 +169,7 @@ Definitions of concrete and abstract PLD's follow.
 Well-formedness conditions for PLD's are separated from this definition, because of 
 practical differences between the way they are used to represent software as opposed to
 representing electronics and mechanical systems.
-The concrete definitions for PLD's and Spider Diagrams\cite{howse:sd} share many common features.
+The concrete definitions for PLD's and Spider Diagrams~\cite{howse:spider} share many common features.
 
 
 \subsection{Concrete PLD Definition}
@@ -178,12 +178,14 @@ A concrete {\em Propositional logic diagram} is a set of labelled {\em contours}
 (closed curves) in the plane (examples of closed curves a,b,c are shown in figure \ref{fig:examplepld}). 
 The minimal regions formed by the closed curves
 can by occupied by `test cases' (represented by asterisks).
-The example diagram in figure \ref{fig:examplepld} has fournumbered test~cases, TC1, TC2, TC3 and TC4.
-The `test cases' may be joined by joining lines. The example diagram (figure \ref{fig:examplepld}) shows two joining lines
-R1 and R2.
+The example diagram in figure \ref{fig:examplepld} has fournumbered test~cases, TC1, TC2, TC3, TC4 and TC4.
+The `test cases' may be joined by joining lines. The example diagram (figure \ref{fig:examplepld}) shows three joining lines
+R1, R2 and R3.
 A group of `test cases' connected by joining lines
-is defined as a `test case disjunction' or Spider.
-Spiders may be labelled.
+is defined as a `test case disjunction' or symptomatically merged group (SMG).
+This is the analog of a `spider' in constraint diagrams~\cite{howse:spider}.
+Joining lines R2 and R3 form a Spider, or symptomatically merged group (SMG).
+%SMGs may be labelled.
 
 %To differentiate these from common Euler diagram notation (normally used to represent set theory)
 %the curves are drawn using dotted and dashed lines.
@@ -297,7 +299,7 @@ Test~cases on the concrete diagram pair-wise connected by a `joining line'
 The graph formed by test~cases connected by joining lines is called an $SMG$.
 %A collection of test cases connected by joining lines, is an  Symptom Merged Group, $SMG$
 %or `test case disjunction'. 
-The $SMG$ is the analog of the Spider in spider/constraint diagrams\ref{howse:sd}.
+The $SMG$ is the analog of the Spider in spider/constraint diagrams\ref{howse:spider}.
 An $SMG$ can be considered to be a collection of test~cases.
 
 {