anchor.diff:      // Convenience operators for manipulating the counter of a MutSlot
       static member (+=) (ms : MutSlot, a) = ms.counter <- ms.counter + a
       static member (-=) (ms : MutSlot, a) = ms.counter <- ms.counter - a
  -    static member (!=) (ms : MutSlot, a) = ms.counter <- a
   
   let rec NextCombination (oldBoard:Board) : Board option =
       // Mutable copy of the deck
  
positive.code: 
      // First lift all the tokens from the last slot
      lifted := mutDeck.[lastPos].counter
      mutDeck.[lastPos] != 0
  
      // Find the right-most token that isn't lifted
      match mutDeck |> Seq.toList
  
negative.code:             while mutDeck.[!pos].counter >= mutDeck.[!pos].max do
                  // Pick up tokens
                  lifted := !lifted + mutDeck.[!pos].counter
                  mutDeck.[!pos].counter <- 0
  
                  // Move one slot to the left
                  pos := !pos - 1
  