Multi-word synonyms are tricky.

You probably want to make sure this synonym is only expanded at index 
time, and not at search time. See some background in the 
SynonymFilterFactory section of 
http://wiki.apache.org/solr/AnalyzersTokenizersTokenFilters

I think the synonym approach is a fine way to search for greek letters 
by name; it's possible some of the new Unicode stuff in Solr 3.1 might 
expand greek letters too, but I think actually probably not (because you 
don't neccesarily want that in the general case), I think synonyms is 
probably your best bet. (Same for things like expanding the musical 
sharp or flat glyph to "sharp" or "flat", which I've considered).

On 5/27/2011 7:43 AM, Thomas Dowling wrote:
> Greetings--
>
> I'm trying to flesh out my synonyms.txt file for a couple of Solr indexes,
> and I stumbled across something weird.  I added these lines to synonyms.txt:
>
> co2, carbon dioxide
> ch4, methane
>
>
> The second line worked as expected: I restarted Solr, reindexed, and could
> search ch4 and methane as synonyms of each other.
>
> The first line did something weird.  Before the change, I can get results
> for both CO2 and for "CARBON DIOXIDE" (just different results).  After the
> change, searching CO2 got zero results, as did "CARBON DIOXIDE".  So at
> least they're acting like synonyms, right?  But why in the world do they
> both stop finding hits?
>
> Pre-change:
>    CO2			225 hits
>    "CARBON DIOXIDE"	130 hits
>    CARBON DIOXIDE	1030 hits
>
> Post-change:
>    CO2			0 hits
>    "CARBON DIOXIDE"	0 hits
>    CARBON DIOXIDE	1030 hits
>
>
> Also, if I want to be able to search for Greek letters by name (alpha,
> beta, etc.), is there a better way than to use synonmyms.txt?
>
>    Δ,δ,delta
>
>
> TIA
>