anchor.diff:  ;; ==> on-value: 4
   ;; ==> on-end
   ----
  +
   
   === Merge
   
  
positive.code: ;; ==> on-end
  ----
  
  === Zip
  
  This combinator combines two observable sequences in one.
  
negative.code:                        #(println "on-end:")))
  ----
  
  The return value of `subscribe` function is a subscription object that identifies
  the current subscription. It can be cancelled executing `(rx/cancel! sub)`.
  
  
  === Consume values
  