You can't really compare two fields.

What you can do, maybe, is the following:
Search field: {template}
Template:
Code:
program: re(field('series'), field('authors'), '')
Search for:
Replace With:
Destination field: series
...
This should use as the source, a template which regexes out the content of the "authors" field from the series field, and then replace the series field with the contents of that source template.