Hi Giuseppe,

The query -0 yields a minus expression with the integer 0 as argument. The result will be the integer 0. You can view the unoptimized query plan by sending the BaseX command "SET COMPPLAN false" (e.g. in the command input panel on top  in the GUI) before running the query.

As Leo indicated, math:log will return a floating point value, which can either be -0 or 0.

Cheers,

Christian