起因是这个问题：
http://zhidao.baidu.com/question/517066465.html?fr=uc_push&push=keyword&oldq=1
我试了一下，我这里也有同样的问题，就上Stackexchange问了一下：
http://mathematica.stackexchange.com/questions/17867/the-shortcut-for-subsuperscript-doesnt-work
可是截止目前，没人能重现这个问题。怎么回事？真是Vista Only？

mma9 ctrl+%没有了？

我这的情况和你在se反映的一样.
window 7 64bit

我认为这不是什么bug，而是使用不当的问题。

先定义了V=9
又计算，结果就是

真要是上下标多，我倒觉得应该使用角标列表更好，像这样不一样吗？
\!\(\*SubscriptBox[\(V\), \({b, bi, bj}\)]\) = 9

@随您进步 突然想到一个可能性。你用的是中文版的Mathematica吗？版本号呢？事件系统呢？

{Subsuperscript[a, x, y], Subscript[a, x]^y,
Subsuperscript[a, x, y] === Subscript[a, x]^y}
ToExpression[SubsuperscriptBox[a, x, y]] // FullForm
ToBoxes[SubsuperscriptBox[a, x, y]]
ToBoxes[Subsuperscript[a, x, y]] // FullForm
参见SubsuperscriptBox

哦哦，在Stackexchange终于有人重现了我的问题了！看样子说不定这会真是这帮认真的老外居然懒汉思维了。
@隨意超 你不把你上面写的这些整理下，在那边贴个答案吗？

已经基本确定是软件本身的问题了。SE上有人建议我去反馈，可是，我没正版的Key，他们不接受我的反馈啊！！！肿么办……要不 @iangie_明月 你去反馈一下？

如果用完整指令Subsuperscript是可以做出一个当符号用的“带上下标的符号”的
========================
我怎么不行?

我也来贴图一幅：

此帖是多么崎岖啊...啊...啊...

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From: "Allison Fry via RT"<[email protected]>
Date: Mon, 21 Jan 2013 10:43:47 -0600
Subject: [WR #288] Support Contact Form: Other
To:
Cc : [email protected]
> The help document of "Subsuperscript"function says that:
> To enter a subsuperscript in a notebook, use either Ctrl+_ to begin a
> regular subscript or Ctrl+^ to begin a regular superscript. After
> typing the first script, use Ctrl+% to move to the opposite script
> position. Ctrl+Space moves out of the subscript or superscript
> position.
> =========
> However, Ctrl+^ can only give a Power to the former variable not a
> regular superscript. The resultant combination can not be assigned
> any value as a normal variable.
> I think this description in the ''more information" of the help
> document of "Subsuperscript" function is wrong.
> Just a feedback, and hopefully this sentence can be removed from
> further version.
>
Hello,
Thank you for taking the time to let us know about this issue in the documentation. I have forwarded this report to our developers in charge of this are of the documentation so that it can be fixed in a future release of Mathematica.
Sincerely,
Technical Support
Wolfram Research, Inc.
http://support.wolfram.com
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劝告搂主不要往这个方向上折腾，立刻放弃这些非常规的用法，回到正途上来

我这里有一个类似的bug:
a = Subscript[a,3]
这会导致Mathematica陷入递归定义，但是a = a3在数学上是一种很常见的做法。
建议MMA把上下标作为一种纯粹的格式定义，而不是函数。