  Polymorphic circuits are a special kind of circuits which possess some
different build-in functions and these functions are activated by environment
parameters, like light and VDD. Some theories have been proposed to guide the
design of polymorphic circuits, including the definition of complete
polymorphic gate sets and algorithms to judge the completeness of a polymorphic
gate set.
  However, the previous algorithms have to enumerate all the polymorphic
signals for judging the completeness of a polymorphic gate set, and it is not
easy to be conducted manually. In this paper, a straightforward method is
proposed to judge the completeness of a polymorphic gate set. And the
correctness of the straightforward method is proved theoretically. Some
examples are given to show that the proposed method could be conducted step by
step. Its actual computing cost is usually low, and it is suitable for manual
operation.
