anchor.diff:  ClassCastException java.lang.String cannot be cast to clojure.lang.Keyword  clojure.lang.Keyword.compareTo (Keyword.java:109)
   ----
   
  -_cc-cmp_ ("cross class compare") below may be useful in such cases.
  +`cc-cmp` ("cross class compare") below may be useful in such cases.
   It can compare values of different types, which it orders based on a string that represents the type of the value.
  -It is not simply _(class x)_, because then numbers like _Integer_ and _Long_ would not be sorted in numeric order.
  +It is not simply `(class x)`, because then numbers like `Integer` and `Long` would not be sorted in numeric order.
   
   [source,clojure]
   ----
  
positive.code: #{["a" 1]}
  ----
  
  Only one element is in the set, because _by-2nd_ treats all three of the vectors as equal. Sets should not contain duplicate elements,
  so the other elements are not added.
  
  A common thought in such a case is to use a boolean comparator function based on _<=_ instead of _<_:
  
  [source, clojure]
  ----
  
negative.code: 
  === Reverse order
  
  To sort numbers in decreasing order, simply write a comparator that calls `compare` with the arguments
  in the opposite order:
  
  [source,clojure]
  