code: def has_transition?(state, symbol)
        return false unless @transitions.has_key? state
        if @transitions[state].has_key? symbol
          actions = @transitions[state][symbol]
          return false if actions['pop'] && @stack.last != actions['pop']
          return true
        else
          return false
        end
      end
docs: Determines whether or not any transition states exist
   given a beginning state and input symbol pair.
  
   @param (see #transition)
   @return [Boolean] Whether or not a transition exists.