A virtual library for SF could be created with this search:
tags:"=Sf" or tags:"=Science-Fiction" or tags:"=Sci-Fi" or tags:"=Science Fiction"
A virtual library for NOT SF could be created with the same search, but with a "not" and parenthesis like this:
not (tags:"=Sf" or tags:"=Science-Fiction" or tags:"=Sci-Fi" or tags:"=Science Fiction")
You would have to recreate, perhaps cut-and-paste, all the searched for all the other VL, put "or" between them and use "not" and parentheses like above.
Anothter way could be to add a tag "In_VL" to all books in each VL in turn, and when done make a VL that is defined with this search:
not tags:"=In_VL"
If you can search for something, you can use it to create a VL.
Assume that you have a custom column named "custom" that holds floating point numbers. Then you can make a VL that contains all books where custom is above 23.3 like this:
#custom:>22.3
You can read more about searches here:
http://manual.calibre-ebook.com/gui....arch-interface