anchor.diff:          member this.Insert element = this.Insert element :> IPriorityQueue<'T>
           member this.TryPeek() = this.TryHead
           member this.Peek() = this.Head
  +        member this.Length = this.Length
   
           member this.TryPop() = 
               match this.TryUncons() with
  
positive.code: ﻿// based on pairing heap published by Okasaki
  // original implementation taken from http://lepensemoi.free.fr/index.php/2009/12/17/pairing-heap
  //J.F. modified
  
  
negative.code: 
      ///returns the first element
      abstract member Peek : unit -> 'T
  
      ///returns the count of the elements
      abstract member Length : int
  
      //returns the option first element and tail
      abstract member TryPop : unit -> ('T * IPriorityQueue<'T>) option
  