[r-t] Complexity of extents

[Matthew Frye]

On 21 Jun 2013, at 23:25, Mark Davies <mark at snowtiger.net> wrote:
> RAS writes,
> 
>> The problem with that is that most general-purpose
>> compression programs (certainly including gzip) don't
>> understand a string occuring once forwards and a second
>> time backwards, e.g. "abcdefghijihgfedcba".  Clearly that
>> string has structure, but gzip doesn't spot it.
> 
> That's a good point. Perhaps it would be sensible to concatenate a reversed copy of the entire string, and compress the combined entity. This ought to produce a higher compression ratio for strings which have reversed elements within them.

But how many cases like this are you going to address? What about back-front symmetry? Rotational? Double? Dealing with them piecemeal isn't really very satisfactory (although the possible symmetries are finite, so we probably could deal with them all this way).

MF