Fraction is centered:

⎡
⎢
⎢
⎢
⎣
12
34
⎤
⎥
⎥
⎥
⎦		× ⎡
⎢
⎢
⎢
⎢
12
34
⎥
⎥
⎥
⎥
⎦
⎛
⎜
⎜
⎜
⎝
12
34
⎞
⎟
⎟
⎟
⎠

You can see arrows:

    
◂
1 × 2 × ⋯ × n
 
  \overleftarrow
    
▸
1 × 2 × ⋯ × n
 
  \overrightarrow

The arrow extends properly

▸
1234567890
 

The arrows extend properly

α  
▸
1234567890
 
  β  
◂
9876543210
 
  γ
This document was translated from LATEX by HEVEA.