RotateLeft
 Usage
• RotateLeft[expr, n]把expr中第n个位置的元素循环移到左边.
• RotateLeft[expr] 把一个位置循环移到左边.
• RotateLeft[expr,   ,  , ...  ] 把依次相连层  位置的元素循环移到左边.
Notes
• RotateLeft[expr, -n] 把n位置旋转到右边.
 Further Examples
This rotates each element one place to the left.
In[1]:=
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Out[1]=
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This rotates each element two places to the left.
In[2]:=
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Out[2]=
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This rotates each element one place to the right.
In[3]:=
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Out[3]=
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