Help with find and replace gui options for renaming many files

Hi and thanks for this. Sorry I omitted to state that Find and Replace was being used in libreoffice calc not Krename.
The text ‘Fermats Last Theorem’ (without the hyphen,) is the subject. If this is the name, it is not formed but the subject of a download. During the downloading process it has been supplemented by other data in a variety of formats which I am trying to remove. Depending on the age of the original there might be a date, characters such as ‘iot,’ dates in other formats and other numbers and letters so using sed would seem a good approach. Can I use this from within libreoffice calc or should I put the data into a text file first?.

If there can be anything then how you expect anyone to write an algorithm to remove it?

You got it backwards. It does not matter whether you use sed, Krename, LibreOffice Calc or anything else - you start with describing rules to perform matching and substitution. Only after you described these rules can you look whether your selected application supports them and if not, you chose another application. You do not start with selecting application expecting that it will read your mind.

Briefly looking at LO help, it seems to support super set of extended regular expressions, so it looks possible to do there (except it is using $ instead of \ for back-references).

I am looking at removing all the data after the text name, ie. the numbers and other characters after text but including the leading space before the numbers but excluding the .mp3.
The majority of lines have a number immediately following the title so I am thinking of using that as the starting logic for writing a rule.
Any exceptions could be sorted out manually.

To become a rule it needs to describe how to find the end of the name.

If “text name” cannot include a digit, it is rather trivial

$ echo 'Fermats Last Theorem 25 Oct 12 iot 20121025-1130a.mp3' | sed -E 's/^([^[:digit:]]+).+$/\1.mp3/'
Fermats Last Theorem .mp3

If “text name” may include a digit, we are back at square one - either you need rules to find out where title ends or you need rules to find out where “junk” starts.

Understood but only a very few names include a number. My problem is that I have been using LO to clean up and sort my data so I want to operate on the column of cells in my spreadsheet. The original text file is more complex and I have been reducing the unwanted or superfluous data in LO. I shall press on. Many thanks.