OK is empty set in failure mode terms for

component failure mode sets

component_failure_modes_definition/component_failure_modes_definition.tex

@@ -753,7 +753,7 @@ create a derived component.
 This technique is outside the scope of this paper.
 }
 {
-This technique is dealt with in descriptions of the FMMD process in chapter \ref{fmmd_complex_comp}.
+This technique is dealt in chapter \ref{fmmd_complex_comp} which shows how derived components may be assembled.
 }
 
 \begin{figure}[h]
@@ -768,7 +768,8 @@ This technique is dealt with in descriptions of the FMMD process in chapter \ref
 Alternatively, we could consider the combinations
 of the failure modes as new failure modes.
 We can model this using an Euler diagram representation of
-an example component with three failure modes $\{ B_1, B_2, B_3, OK \}$ see figure \ref{fig:combco}.
+an example component with three failure modes\footnote{OK is really the empty set, but the term OK is more meaningful in
+the context of component failure modes} $\{ B_1, B_2, B_3, OK \}$ see figure \ref{fig:combco}.
 
 For the purpose of example let us consider $\{ B_2, B_3 \}$
 to be intrinsically mutually exclusive, but $B_1$ to be independent.