Update chapters/functions.tex

Co-authored-by: Henrik Tidefelt <henrikt@wolfram.com>

chapters/functions.tex

@@ -1632,7 +1632,7 @@ \subsection{Partial Derivatives of Functions}\label{partial-derivatives-of-funct
 is the partial derivative of a function, and may only be used as declarations of functions.
 
 The semantics is that a function (and only a function) can be specified in this form, defining that it is the partial derivative of the function to the right of the equal sign (looked up in the same way as a short class definition, and the looked up name must be a function), and partially differentiated with respect to each {\lstinline!IDENT!} in order (starting from the first one).
-The {\lstinline!IDENT!} must be scalar {\lstinline!Real!} inputs to the function.
+Each {\lstinline!IDENT!} must be a scalar {\lstinline!Real!} input to the function.
 
 The comment allows a user to comment the function (in the info-layer and as one-line description, and as icon).