First
 Usage
• First[expr] 给出 expr中的第一个元素。
Notes
• First[expr] 等于 expr[[1]]. • 参见 Mathematica 全书: 1.8.4节.
 Further Examples
This gives the first element from the list.
In[1]:=
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Out[1]=
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The result may seem strange until you see how the polynomial is stored internally.
In[2]:=
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Out[2]=
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In[3]:=
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Out[3]//FullForm=
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