complete previously-writen-to-file inline maths elsewhere

I: anywhere with ```$ [space] [part-of-eq] Ctrl-x Ctrl-o```
II: after ``` \(, \[ or \begin{eq-env}``` with ```[space] [part-of-eq] Ctrl-x Ctrl-o``` in the same line or other lines followed

ATTENTION: 
1, only try to match form the writen-to-file eqs. 
2, CONFLICT: after using this, we can only complete eq-env by first typing ```\end{``` fully 


Example
```
\documentclass{report}
\begin{document}

You type here:
$\mu$, $hello$, \(world\)

% Note: contents in [...] are optional

You still need it in the following cases:

Dollar one, all in single line 
$ [some-space][part-of-\mu] Ctrl-x Ctrl-o

Parenthesis / bracket, single or multi lines
\( [some-space][part-of-\mu] Ctrl-x Ctrl-o
\(  \mu and  many more: [some-space][part-of-\mu] Ctrl-x Ctrl-o   \)

\(
some other math here,  some-space-here [part-of-\mu] Ctrl-x Ctrl-o, then go to next lines
some-space-here [part-of-\mu] Ctrl-x Ctrl-o

In eq env
\begin{equation}
    some other math...
    [some-space][part-of-\mu] Ctrl-x Ctrl-o

% the sad point: we can no longer complete \end{eq-env} here with [\end]Ctrl-x Ctrl-o
\end{equation}

$\mu$ 

ATTENTION: don't expect to have mu in the following:
(for the dollar case, it just works in single line)
%%%%%%%%%%%%%
$
some-maths here, [some-space][part-of-\mu] Ctrl-x Ctrl-o
%%%%%%%%%%%%%

\end{document}

```