If a biblio title contains the hyphen character "–" / \xE28093 and you try to search the title as it is written with the hyphen the search produces no results. I think we need to add hyphen to the list of punctuation characters to ignore to fix this problem. The file is in admin/searchengine/elasticsearch/index_config.yaml The issue could probably fixed also by removing hyphen in the tokenization step when storing the record to the index?
In Elastic Search a hyphen operates as an 'or'. Trying to search for a term like steam-boiler will return results where the term steam or boiler exists. In order to get correct search results add quotation marks "steam-boiler" to force Elastic Search to see it as a single term. Another example is to search for U-2 boats using U2 rather than U-2. U2 is a single term but it is not returning the expected results because U2 doesn't match "U-2" or U or a 2. One option is to add U2 to a 246 varying title tag so that it appears in search results. I think in this case Elastic Search is working the way it was designed. The question is should Koha make an exception to using the hyphen as a boolean operator?
I can see that this could be quite an issue for German as well as we do have a lot of words that are hyphenated.