Doc fixes from John Belmonte.

doc/guide/modules.tex

@@ -142,12 +142,12 @@ almost never used -- best to consider it deprecated).
 % XXX set functions have complicated behavior.
 Each of the modules also defines some functions that operate on
 BTrees -- \function{difference()}, \function{union()}, and
-\function{difference()}.  The \function{difference()} function returns
+\function{intersection()}.  The \function{difference()} function returns
 a bucket, while the other two methods return a set.
 If the keys are integers, then the module also defines
 \function{multiunion()}.  If the values are integers, then the module
 also defines \function{weightedIntersection()} and
-\function{weighterUnion()}.  The function doc strings describe each
+\function{weightedUnion()}.  The function doc strings describe each
 function briefly.
 
 \subsubsection{Total Ordering and Persistence}