Turn see-also index entry into textual cross-reference

As requested by Hans.

chapters/classes.tex

@@ -202,7 +202,8 @@ \subsection{Component Declaration Static Semantics}\label{component-declaration-
 
 \subsubsection{Declaration Equations}\label{declaration-equations}
 
-An environment that defines the value of a component of built-in type is said to define a \firstuse{declaration equation}\index{declaration equation!zzzzz@\igobble |seealso{binding equation}} associated with the declared component.
+An environment that defines the value of a component of built-in type is said to define a \firstuse{declaration equation} associated with the declared component.
+These are a subset of the binding equations, see \cref{equation-categories}.
 % Note: In variability-of-expressions, it's called a "binding equation", not "declaration equation".
 The declaration equation is of the form \lstinline!x = expression! defined by a component declaration, where \lstinline!expression! must not have higher variability than the declared component \lstinline!x! (see \cref{variability-of-expressions}).
 Unlike other equations, a declaration equation can be overridden (replaced or removed) by an element modification.

preamble.tex

@@ -90,6 +90,8 @@
 
 % For solving issue with see-also entries in index, see
 % - https://tex.stackexchange.com/questions/231840/what-is-the-proper-use-of-several-seealso-in-the-same-index-entry-with-makeinde
+% For example, this is how to create a see-also item under "declaration equation":
+%   \index{declaration equation!zzzzz@\igobble |seealso{binding equation}}
 \def\igobble#1 {}
 
 % Providing command that other authors seem to take for granted.