[clug] OT meta-regex question

[Gough, Chris]

>> On Tue, 3 Feb 2004, Gough, Chris wrote:
>>  A = '^.*$'
>>  B = '^foo$'
> and Michael Still replied:
>
> For this simplistic example, you can just strip common starting and
> trailling elements, and then ask if:
>
> .* could match foo
>
> Here the answer is yes. This simple technique falls apart for more complex
> examples though:
<snip>

That's pretty neat. If I manage to reduce one of the regexes to a 'plain
string' before running out of common starting and ending elements, then the
answer I want is the same as:

  does 'remaining regex with possible wildcards' match 'plain string'? easy.

But in cases where I can't reduce at least one of the regexes to a plain
string by stripping common starting and ending elements, I am still left
with my first problem:

  is there a string that will be matched by both regexes? still too hard for
me :(

Can you think of any other tricks like this?

If I keep collecting such tricks, am I going to be able to make a general
solution, or is there always going to be some unsolvable regex pairs?


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