code: func (b *BoundedMemoryChain) Back() *Node {
  	if b.tailPtr == -1 && b.headPtr == -1 {
  		return nil
  	}
  
  	return &b.chain[b.tailPtr]
  }
docs: // Back returns the end of the chain. If the chain is empty, then this return a
  // pointer to a nil node.
  //
  // NOTE: Part of the Chain interface.