Stress continuity of function arguments

Co-authored-by: Hans Olsson <HansOlsson@users.noreply.github.com>

chapters/functions.tex

@@ -1230,8 +1230,8 @@ \section{Derivatives and Inverses of Functions}\label{derivatives-and-inverses-o
 This means that the function is at least C\textsuperscript{smoothOrder}.
 
 When a tool computes the derivative of a function, e.g., for index reduction or to compute an analytic Jacobian, each differentiation of a function reduces the \lstinline!smoothOrder! by 1.
-The \lstinline!smoothOrder! information can then be used to infer continuity of the resulting differentiated function calls.
-This is a conservative check, however, meaning that a tool may be able to establish continuity of a function call even though the \lstinline!smoothOrder! has been reduced to less than 0.
+The \lstinline!smoothOrder! information can then be used to infer continuity of the resulting differentiated function calls, provided the input arguments are continuous.
+This is a conservative check, however, meaning that a tool may be able to establish continuity of a function call even though the \lstinline!smoothOrder! has been reduced to less than 0, and/or some input arguments are not continuous.
 \end{nonnormative}
 
 The optional argument {\lstinline!normallyConstant!} of {\lstinline!smoothOrder!} defines that the function argument {\lstinline!IDENT!} is usually constant.