docs: fix headings

docs/language/learn-ql/cpp/value-numbering-hash-cons.rst

@@ -62,8 +62,8 @@ Why not a predicate?
 
 The obvious interface for this library would be a predicate ``equivalent(Expr e1, Expr e2)``. However, this predicate would be very large, with a quadratic number of rows for each set of equivalent expressions. By using a class as an intermediate step, the number of rows can be kept linear, and therefore can be cached.
 
- Example queries
-~~~~~~~~~~~~~~~
+Example query
+~~~~~~~~~~~~~
 
 This query uses the ``GVN`` class to identify calls to ``strncpy`` where the size argument is derived from the source rather than the destination
 
@@ -95,8 +95,8 @@ The hash consing library exposes its interface primarily through the ``HashCons`
 
 To get the ``HashCons`` of an ``Expr``, use the ``hashCons`` predicate.
 
-Examples
-~~~~~~~~
+Example query
+~~~~~~~~~~~~~
 
 .. TODO: prose explanations