从双代数的定义入手，给出了双代数成为交换和余交换双代数的两个充分条件。
We study the definition of bialgebra and prove the sufficient conditions about a bialgebra is commutative and cocommutative.
学习英语词汇除了从词汇的语音、拼写和一般定义入手外，还应特别注意词汇的语义。
Besides, learning English words begins from their pronunciation, spelling and basic definition, and the semantic meaning of word should especially be paid attention to.
学习英语词汇除了从读音、拼写及一般定义入手外，还应特别注意词的语义关系这一因素。
As we study English words, we should pay special attention to semantic relationships of words besides beginning with pronunciation, spelling and general meaning of words.
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